Ok, first ride feedback.
1. Width (730) felt pretty good in general in terms of fit.
2. Stem was actually 80mm (thought it was 70), and I didn't notice any real difference in reach from my current 90mm.
3. Clipped a tree on Towai Traverse, rode that and 491 as they're probably the tightest I normally ride. No real damage, skinned my knuckle. Pain is a good way to calibrate I guess.
4. Steering definitely felt slower and more deliberate, but certainly felt the extra leverage.
Will definitely try a shorter stem (hopefully got a 60mm on the way soon), and know that I definitely need a riser bar with similar upsweep to what I currently ride. My first test bar is flat with no upsweep, lost 40mm off my bar height and certainly felt it.
Interesting experiment so far - not jumping to any big conclusions after just one ride though. Wider certainly felt good on Super Plus - fast and a bit less toight.
Pity my shoe assoloded right at the start of the ride. An SPD jandal isn't much fun when you need to unclip in a hurry...