I am surprised nobody has blasted, I mean reponded to this e-mail.
Anyway, on to your questions.
Frankly, a guy your size should be a 'no-brainer' for 29" wheels, but your experience may vary.
No experience with a Fisher 29 personally, but I find the climbing ability of my 29" bike equal to or better than my 26" bike (these are both SS however, if that makes a difference).
There has been some issue with certain Fisher frames cracking; not exactly sure which ones.
Might want to search and find out, as you are plenty stout at your size.
Also, there are other 29" options available (on a budget mind you) for a clyde like yourself.
As far as the wheel flex.
I think that you can have a pretty bombproof/stiff set of wheels built depending on what your desired weight to strength ratio is.
The Kris Holm (sp?) unicycle rim is apparently indestructible...........but a bit portly.
May not matter to a guy your size though.
Do a user search on Mikesee and you will probably find more than you need to know to make a decision on wheels.
Most, if not all on this forum have embraced the 29er standard. Some even sell off all of their 26" bikes shortly therafter.
Few that I have seen, actually go back to the traditional sized wheels.
Personally, I will likely keep only a 26" FS for those 'special days'.
Otherwise, 29" is the ticket for me.
Good luck, whatever you end up on.
I'm looking into buying one of the Fisher 29's. I have 2 questions about the 29" experience. First: Are there any drawbacks in a bike's ability to climb due to the larger 29" wheels/tires ? Second: What about wheel flex ? I'm 6' 3" and weight 230 lbs. Could my weight be a problem on rough trails ?