ROAD
shimano 8 speed triple crankset
Shimano Deore FC-M532 26/36/48 crank. Price was around $120-130 and the bottom bracket was included. Looks like the successor to the M532 is the Shimano FC-M590 crank.
Shimano FC-M590 Deore Triple Crankset - 9 Speed SG-X chainring
With the capability to use MTB-type RDs with STI and any other levers, I don't see any reason to use road derailleurs on a touring bike. The 9-speed XT RDs ("Shadow" and regular) have a 45t capacity with the SGS long cage, which is pretty impressive. Even the 9-speed Deore M591 will handle the 45t wrap.
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About the only incompatibility is with the newest 10 speed Shimano mountain bike rear derailleurs. They do not work with road 10 speed STI shifters. But older 9 speed mountain bike rear derailleurs work fine with road STI shifters of any gearing, 7-8-9-10. Shimano 9 speed mountain bike rear derailleurs are really cheap, $20 Deore. So no reason not to use one. Low end Shimano front derailleurs, Sora, Tiagra, are also really cheap, $15. So no reason not to use those either.
You've mentioned using your left front STI Shimano 105 shifter to shift a triple crankset. It shifts a compact double crankset now. I'm not so sure Shimano STI can shift both double and triple. Shimano makes unique double and triple STI shifters in Ultegra and 105 models. So I'm questioning whether your crankset change will be as smooth as you are implying. I think you will need a new left STI shifter for the triple crankset.
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COMPACT DOUBLE CRANK (48/34): Shifters (10 speed STI) + Compact double crank (48/34) + Cassette (10 speed 36T) + Rear derailleur (Deore 9 speed) + Front derailleur (road double). GI (38mm) = 25.8 - 119.8
The Deore derailleur is needed to shift to 36T (road derailleurs only go to 34T)
On the Giant Revolt, this would mean: Keep the shifters, compact double crank, and front derailleur; Get a 36T cassette and Deore 9 speed derailleur. This only lowers it from 34T to 36T, and the lowering of GI is from 27.5 to 25.8 = 1.7 GI. Not much.
SUPER COMPACT DOUBLE CRANK (46/30): Shifters (10 speed STI) + Super compact double crank (46/30) + Cassette (10 speed 36T) + Rear derailleur (Deore 9 speed) + Front derailleur (road double)
The road front derailleur has a max difference of 16T, so this is ok.
On the Giant Revolt, this would mean: Keep the shifters and front derailleur. Get a super compact crank (e.g., VO), a 36T cassette, and Deore 9 speed derailleur. This lowers the small chainring from 34T to 30T and the cassette from 34T to 36T. The lowering of GI is from 27.5 to 22.8 = 4.7 GI.
Compatibility checks:
(1) Ability to lower the FD clamp to accommodate 46/30.
(2) Ability of FD to shift 46/30
(3) Compatibility of 46/30 with 11-36
(4) Compatibility of STI with Deore 9sp derailleur
Cost: Super compact crank (e.g., VO = $200), a 36T cassette (= 70), and Deore 9 speed derailleur (= 70). Total = 340.
TRIPLE CRANK (48-36-26 or 46-36-26): Shifters (10 speed STI) + Touring triple crank (48/36/26) + Cassette (9 speed 34T or 10 speed 36T) + Rear derailleur (Deore 9 speed) + Front derailleur (triple)
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Does a shimano deore 9 speed rear derailleur shift a 10 speed cassette?
Another useful fact: this derailleur will work with recent Shimano 10 speed cassettes shifted with Shimano STI brake/shift combined levers. It sounds counter intuitive, I know, but the activation ratio matches correctly for this combination, too. 10-speed STI does not use the same ratio as 10-speed MTB thumb shifters - it retains the older ratio. I bought a second rear derailleur in case I want to put an 11-36 10 speed cassette on my 2010 Ultegra STI equipped road bike for use in steep mountains.
*With 36t large cog, you might need a longer B tension screw (see related items) to keep the derailleur cage away from the large cog.
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Shimano 10 spd STI shifters (Ultegra and 105) with the new SLX 10 spd 11-36 cassette.
We used SLX 11-36 10 spd cassettes, although I don't see any reason why the XT 10 spd cassette wouldn't work just as well if not better.
We used 9 spd Shadow rear derailleurs, an XT on one and an SLX on the other. This is VERY important: you CANNOT use the new 10 spd Dyna-Sys rear derailleurs, they won't work with 10 spd STI shifters! If you're going with a 36t cassette, like we did, you must go with the Shadow rear derailleur (I used the XT RD-M772 on my gf's bike). Shimanospecifications say that these derailleurs are designed to work only up to a 34t cassette, but both worked the 36t cassette just fine and with room to spare.
If you're going with a 10 spd 11-34 cassette then your derailleur choices may open up some, but you still must use a 9 spd rear derailleur.
The 10 spd mountain cassettes only work on 8/9/10 freehubs, and will NOT work on freehubs made made to work only with 10 spd road cassettes.
The road front derailleurs were not designed to shift the odd chain angle when you go from your middle chainring (such as your 42 or, in the case with my gf's bike, a 39) to the 30t ring while in the 36t cassette. This means that the front derailleur limit screw adjustment is very touchy. If you can, it's a good idea for insurance purposes and to make life a little simpler, to add a chain watcher of some sort. We've had success with the N-Gear chain watcher on a different bike, but I'm still searching for a chain watcher that will work with either or both of these frames. There is a well made one other there (I forget the brand) but it costs between $45 and $60, so for now I'll see how things go. Right now both bikes are shifting to the 30t ring just fine.
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I like Mike Sherman's Gear Calculator. It updates all the charts on the fly as you make changes.
You can quickly see what happens when you change to smaller chainrings.
This Speed over RPM Range chart is very good for showing ranges for each chainring. Each chainring is a different color.