SRAM XX1 11 Speed Rear Mech Technologies:
- X-Actuation - Designed specifically for SRAM XX1, X-Actuation keeps shifting sharp and consistent across the entire 10-42T cassette.
- X-Sync - A "wide tooth, narrow tooth" pattern is repeated around the pulley wheel, perfectly mirroring the chain's inner and outer links for maximum control.
- Cage Lock - With Cage Lock, wheel removal and installation - becomes faster and simpler. Just pushing the cage forward to create slack and lock it into place.
- Roller Bearing Clutch - Roller bearing clutch technology eliminates derailleur bounce and chain slap without sacrificing precision.
- X-Horizon - Straight parallelogram design limits all movement to the horizontal axis, which makes ghost shifting impossible while also reducing shift force. For quicker, more exact shifting, the large upper pulley offset design maintains a constant chain gap across all gears.

42t sprocket is huge and it can apparently be as large as 44T. With a sprocket that large there should not be an issue with the RD cage striking the spokes ...

So one could run 10-44T cassette with 44/46T crankring for a road setup, although the largest crankring for the MTB setup is 38T

10 instead of 11 saves 5 teeth from the front, 10 instead of 12 saves 9 teeth from the front. So if I feel the need for 53/12, for example, I can drop to 44/10 at the same ratio. Meanwhile 44/42 is the same as 34/32 so the 10-44 gives the same range as a 34-53/12-32. That's hugh. Only issue is the jumps, for example: 10-12-14-16-18- 21-24-27-31-36-42 would work well, I think: big top end gear just for descents, then decent spacing through the cruising gears, then bail out gears at the bottom end. These aren't racing ratios but would work well for Gran Fondo type riding.

This is slightly off topic, but I'm intrigued how that shop can have a cassette for XX1 in stock but the derailleur isn't available until the end of April?

@ultimobici:
djconnel is suggesting a single chainring (44T) combined with a 10-42 cassette.