SOMDStang is correct....it's best to add supercharger upfront before investing into a ton of mods if you want to "stay up" with GT's. My heavy V6 convertible auto is fast (low 6 sec 0-60 w/over $3,000 invested) with slicks, but if I want to stay even/outrun GT's I have to spend $5,000 for my "finish mod" supercharger. At that point I'm way over max NADA value for my Mustang, so if I wreck it and it's totalled, the insurance company won't pay off the entire loan.
If someone wants GT power then it's always best to purchase a GT. For me, I like "underdog" cars, in other words, 6 cylinders that can stay up and or outrun their bigger brother V8's. I'm building that right now with my V6 and I've currently spent the dollars to have the ground work laid. My final "cog" in the machine is the supercharger which should get me in the very low 5's for 0-60. However, even with the supercharger, my times will be equal or just a little quicker than the V8.
The moral of the story is, if you like working on cars and spending money, then a V6 build will be loads of fun. The satisfaction comes in when you outrun those (mostly stock) V8's and you tell them "it's a V8" the look of "pure shock and disbelief" is priceless! If you're a buyer that likes fast cars and "on the fence" between the V6 and V8, my advise is to spend the money and get the V8. Otherwise, you'll be kicking yourself everytime you get in that V6; regret is on of the worst of human emotions. For myself, I have zero regrets about my V6! I have the convertible that I wanted and have had an awesome time modding it....getting to the point where it is today. However, my "perspective" is different than most of you young bucks on these forums. I grew up driving/racing 80's and 90's Mustang V8's and my 07 modded V6 is every bit a quick as those (except for my 1991 Mustang 5.0 LX AND Cobra's not included in my assessment!).....I'm a happy camper!
Cheers!
Jedi