I have a set of 29" Flows and a set of Arches in 26" & 29". This'll be the 4th season for the Flows; they've seen the most use by far and I've had no issues with any of 'em...the 26" Arches haven't seen much use at all since they're on the wife's bike.

The Flows have been bombproof for me. I've ridden that set all over the country - Moab, Colorado, Kansas City, Wisconsin - and they're as true as the day I got 'em. A lot of that is a testament to the quality and craftsmanship of the wheel builder, but credit should also be given to the components. The same guy built the Arch/Hope set - this wheel set sees use primarily on my Niner for racing and general trail riding throughout the dry season and, like the Flows, they have been great for me. This year will be the 3rd season for this set and they're still as true as the day I unboxed 'em. The Arches feel "livelier" (?) and are definitely faster but I wouldn't punish them the same as I would the Flows. Definitely a different feel between the 2 sets.

I can't comment on any experience with the P35s but I do know they have a great reputation for durability and reliability.

I can comment on WTB. I replaced a set of LaserDisc29 w/LaserLite hubs with the Flows/Hope hubs combo. The WTB set was silly flexy. I couldn't stand it. From what I've read lately, they've come along way with their new stuff. Personally, I will stay away from WTB wheelsets based on my prior experience.

As far as hubs go, if you're looking for alternatives to the SLX and XTs, take a look at the the DT Swiss 350. They're made with the same internals as the highly regarded and much more expensive 240 hub, but with slightly heavier and less expensive materials. If you can find a good deal on the 350s, you can't go wrong.

You building the wheels yourself?