Bit of an update.......
After several cog changes and many a test ride, I'm back to using the 7th<>10th cogs of the stock Shimano XT 11-36 cassette ie. 24/21/19/17/15/13/11
Reasons being as most of my riding is done on this part of the cassette and I was trying to close up the gap created by removing the 17/15t and substituting it with a 16t cog....
I'm now settling on making the cog swap in the 2nd<>3rd cogs with either 41-(36/28t), 41-(36/30t) or 41-(34/28t)....basically my 3 granny gears.
It's interesting putting numbers into gear calculators and then riding the spread to find that it doesn't always work for you in the dirt, though looking good by the numbers....
Also Wombat, what amazes me is how tolerant the 10spd system is when it comes to cog spacing and a mix of eBay/10/9spd cogs.....there's been a few times when I've been hard up for spacers and I've run what I've had....again with shifting that's been close to standard.
On the subject of freehub marking this could be an issue for some brands, my Hopes are marked by the standard cassettes so this is something I accept....I may upgrade to their steel freehubs but will monitor.
Now XX1's cassette....I do see a good possibility that more cog spreads might be needed/wanted than the current cassette. Especially those who like a closer ratio 5<>11th gear..
Anyway, in the end I'm pretty happy with what I'm running on both bikes but do look forward to the time when Shimano respond....albeit it a little too late if SRAM X9/7 their XX1...