Yeah, sorta what I thought. I've been exchanging email with the tire folks who've assured me that the 990/606/908 combination is no problem for the UHD tubes despite the earlier warnings.
But I do question the UHD paradigm. I've run them for years on the 525, but the big bike is different. The 606 run on the smaller bike carries a load of something like 275 lbs at fairly low sustained speeds. The same 606 on the big bike will carry closer to 375 at much higher sustained.
Further, the small bike will be lower psi- I usually run about 10-13. I think if I run that low pressure on the big bike (off road), I'll be buying a new front rim pretty quick.
Do I really gain a lot of flat protection with the thicker tubes?
Thanks for all the input so far, keep it moving!