My 2 cents is to buy the 450. I am 6'3" and 280 and I got a 07 on sale 2 months ago. I put a toggle switch on my grey wire to be able to calm it down on super tight single trails, and did all the free mods and the quiet end cap on exhaust. I am glad I rode it awhile before doing the mods, could have hurt myself until I got used to it. Also, we probably all need to redo the springs for our weight, unless you weigh nothing, or like it soft.
Thank you for finally mentioning suspension. But so far I have everyone beat! 6'2" 285 lbs of man-beast. Without a doubt, go fo-fiddy. Unless of course you have a 150 lb nephew you want to give your 6 month old 250 to. Just be careful for the first bit until you think your ready for all the glory that is the WR450! The best money spent on mods will be the springs and re-valving and a Scotts stabilizer.