If leaving stock, then the 96-98 will be faster. Even adding a SC to a stock Cobra, the 96-98 will be faster. But there is only so much that can be done to a 4.6 motor. A 5.0 can add heads, intake along with the other items that can be done the the 4.6, ie cams, forged internals. The 5.0 would be cheaper to buy & mod.