That and there is not much to do to a 4.6 NA. Cams dont make enough of a difference on the 96-98s (usually 2 hp for $1000+). CAI for some absurd reason is double the GTs price.
But headers, h-pipe, cat back, tune, gears are all the same price as the pushrods
A 4.6 DOHC will give you 400 rwhp on a street car with a bore and stroke and some head work.
A 5.0 will be similar with the same mods (but more displacment).
Now boost is another story all together. If you took a box stock Cobra and added forged pistons/rods and a blower/turbo the engine can make 750+ rwhp all day lomg and be reliable as a stock car. Cant do that with a stock 5.0 engine, it will split in half. So you figure a DART (or similar) block with heads and forged internals, intake, cam and turbo/supercharger to get to that same HP level and you will have spent double what you would be into the Cobra.
Difference is the 4.6 can still be driven easily on the street and can withstand another 450+ hp before you have to worry about failure.
Teksid DOHC > *