I can't find the link right now, but Michael Alden over at the London Lounge wrote a great article about wearing lighter colours, in which a "gentleman of stature" complained that lighter colours weren't as slimming. Mr. Alden replied something to the effect of "So what?" The trick, he argues, is to embrace your size and stature, rather than trying to hide it. Exercise and diet, of course, are necessary if one wants to change, but dressing how you wish and wearing your clothing comfortably and with confidence is what really makes a man stylish.
All that being said, I'm 6'4" and about 265lbs. I'm generally the only one in my vicinity in a suit or jacket, and dress as such regularly. I like being a big guy, and especially like being a well-dressed one.