I don't know if the longtubes would be worth it at this point in time. For the sake of argument, I'll throw in another $.02 (which is about all it's worth
).
1. It's a stock mustang, which in my opinion, isn't worth the hassle of the install (especially since it's a sn95 = less room under the hood). Also, we don't know what mods (if any) are planned for the future.
2. We don't know what transmission is in the car. Do they make longtubes that fit around the AOD? Also, If it has a manual tranny, there's the possibility of melting clutch cables.
3. Longtubes may throw off the readings from the o2 sensors since they are located farther downstream than stock (ie exhaust gases being too cool). Even though they work well on your car, does not necessarily mean that they will work on someone elses. My check engine light used to come on all the time due to the absence of catalytic converters. But for some reason, it hasn't came on at all since my head/cam swap. Go figure!
If it were my decision, I would go with the unequal shorties, off-road h, and flowmasters.