Gearing analysis:
Going by my experience on my CRX2, the lowest gear I had and occasionally needed was 31GI (gear-inches). The highest gear I had on it was 116GI. However, I pnly used this gear going downhill when I wanted a rest but still wanted to pedal, so just spinning legs but no effort given. I don't compete, so I don't really need this gear, and here is only a small amount of difference for me between pedalling or going into an aero tuck.
If I really want to put a big effort, I spin at perhaps 90RPM; with a 58Tx11T gear combination this gives about 40km/h (25mph), adequate for most cases. Higher speeds require higher than 90rpm, easily given during short bursts. Using a 11-34 cassette, the lowest gear is then 32GI, very close to what I am used to needing on the slopes. That small difference is negligible for me.
This leaves me in the clear to select a 11-34 cassette with 58T ring. The alternative is to use a road cassette, say 11-23, plus 2 chainrings 48T-60T, with a derailer which I would have to custom mount due to the large seat tube diameter.
Calculating the extra weight from the extra chain ring, flat bar XT shifter, cable+housing, front derailer, gives an extra weight of about 350g over the single ring solution, plus perhaps another $100 easily. All this for closer spaced gearing. The money saved could be put into XTR componentry, saving perhaps another 100g, making up almost half a kilo.
All this is weight weenie stuff, but it does make a difference if you're a keen climber. So I will go the single ring way.