If you're planning a big trip, I'd stick with what you know. At least bring your Xpan as backup.
I totally second that advice.
- The largest sensors currently available on one shot digital backs are 36*48 mm. The top contenders in terms of resolution are the Leaf 75, Phase P45 and Hassy H2D39/H3D39. If you need wider, then scanning solutions from Betterlight on 4x5 are basically the only solution, but it comes at a price in terms of convenience,
- I find A2 prints (17x22) made from a 22 MP back (Mamiya ZD, Phase 25, Leaf 22, Sinar 22,...) to be difficult to distinguish from Imacon scanned 4x5,
- A problem sometimes seen with 35 mm DSLR - and still present to some extend with higher end digital, is the rendition of the sun edges or other transitions to very bright areas. Digital backs are not totally free of that, but are significantly better than 35 mm DSLR,