If anything it will increase handling because you'll have more rubber on the road. IMO anyway. As far as performance losses, I dont really see where you are coming from. The only thing that I can think of is having a bigger, heavier wheel, so it doesn't take off as fast. However, 10 hole wheels are aluminum, where as the polycast ones you probably have are not. So the weight may actually be quite similar.
Having larger tires on your drive wheels will change your overall gear ratio (as seen thru roll-out) this will make your engine work harder to accelerate, however it will actually lower your rpm's at highway speeds, so it should woork easier to keep the car at 65mph (or 95 if your like me sometimes... )
Roll-out: the distance your car travels from one revolution of the engine excluding free rolling. it can be seen mathematically thru this equasion--
(tire diameter x 3.1416)
--------------------------------------- = ROLL-OUT
(transmission ratio x rear-end gear ratio)
Only taking top gear into this equasion let's say 1:1 is top gear which would be simply 1 and your rear has 3.73:1 which would be 3.73 so
1 x 3.73 = 3.73
And your old tires where 25.5 inches tall and your new ones are 36 inches tall (exageration) So--
old tires 25.5 x 3.1416 = 80.1106
new tires 36 x 3.1416 = 113.0976
divide each by 3.73 and you get
old tires rolls-out at 21.48 inches per engine revolution
new tires rolls-out at 30.32 inches per engine revolution
I know most people find this useless, but I also know somebody would blast me for saying it changed your gear ratio since you aren't changing any gears....... Plus I also find the mathematics of cars interesting (I know I'm a geek :damnit: )
Also your speedo will always read slower than what you are actually traveling, and your odometer will be off as well. This can be fixed and a good transmission shop should be able to switch out your speedo drive gears in the tranny for around $20-$30 and it shouldn't take more than an hour...
Switching out the 14" granny wheels for 16" was probably one of the best changes i made to my car. Not only does it look a helluva lot better, the ride is 10 times better. I have 225/55's on mine it has such a nice stance now. My car used to shake like a mofo anything over 65 mph, now it rides really smooth for a fox convertible. Also a lot better going around bends.