would be good, the 4.0 can handle a 75 shot (75 to the wheels/100 crank) without a tune with no problem, Autos with this have run as low as 13.1 in the 1/4 with drag radials. I believe Americanmuscle.com has them on sale for $58 bucks right now.
Other than that there's a Vortech supercharger on the same website for $3400 that will add about 90 HP to the wheels.
Then of course there's bolt ons (air intake, exhaust, tune, and rear end gears with trac loc) that will all together shave about 1.1 seconds off the 1/4 mile time, but if you do the math the nitrous is the most cost effective and it's only there if you need it.
I went the bolt on route and am pretty happy with the performance, best 0-60 is 5.8 best 1/4 mile is 13.8
2008 4.0 SOLD (I will miss my first stang forever)
2011 5.0 black on black with 3.73 manual
and I still get over 26 mpg