I think he might mean on a sawblade... I don't think you can put a 255 on a sawblade unless it's at least a 50 series tire. The overall diameter/height would be more than an inch taller than the stock 225/50/16 setup, but that's only about a 5% speedo error.
I'm not sure just how much tire height makes a difference, but I gained like 0.1" in diameter when I put on 225/45/17 over stock and I noticed even that helps me clear some bumps easier than when I had the sawblades on.
There's a pretty cool wheel/tire comparison and calculator website that has gearing and fitment here:
http://gs.tolan-hoechst.com/tirecalc.htm
I think 225s will still be enough for me for some time... i just need some damn spacers for them, or at least for the fronts. oh well, still better than the sawblades!