Your math looks good. The difference isn't huge, but there will be a slight lag in acceleration and your speedometer may be off by about 1mph around the 80mph mark. But neither of these will be truly noticeable.
That'll fit, any professional shop won't have a problem with it. You'll have a bit more bulge in the sidewall, but that's extra protection for your wheels.Thanks. The other concern I would have would be trying to go to a 235 on a 7 inch wide wheel later. Would that work?