Lt1's are not that fast, and are complete POS's IMO. I ran with an LT1 on a 0 to 60-70mph sprint in my last 5.0, which had a 5 spd, full exhaust and stock 2:73 gears. His auto LT1 had a cat back and a CAI. When we shut it down, the nose my stang was even with his front tire, basically a tie, and I did not powershift. I was not impressed. True, he had an automatic and I had a 5 spd, but I had 2:73 gears, and was giving up 50 cubic inchs, and lost by less than 1/2 a car length. Not impressed.
Not to mention, LT1's:
Look like ass
Are a B**ch to work on
Have various problems (Not that 5.0's don't have a few quirks, but not nearly as bad as LT1's)
Parts are more expensive
Horrible hump inside car
Handles, feels like a rattle trap POS when driving/riding in one.
Interior ergonomics such ass
...etc...
LS1's share many of the same "Camero turn off's", but are MUCH better cars overall, and are MUCH faster, but obviously cost a lot more $$$.
LT1's arent that impressive, but the LS1's are a lot faster. A simple mod on your mustang and it'll have with LT1's all day long, takes a few more to keep up with the LS's though.