It's not just a function of getting the tire ON the wheel, it's the profile that results. A 45 series tire is going to generally be less forgiving of less-than-optimal wheel width, creating a funky profile that doesn't put the tread on the track as anticipated.

Check with PhilTireService.com and see what he recommends but I'd be surprised to find out that a taller tire makes you faster, unless you are running out of revs in 5th someplace, for more than a little while...

K