What kind of sound are you going for? Loud? Rumbly?
The SLP will be nascar loud. The Flows will be more rumbly without the blarring loudness.
My suggestion, because chokemasters are horrible and cheap...is either get magnaflows (~$450) or the SLPs if you are going for the loud sound.
X-Pipe, I would go with the UPR x-pipe instead. Never heard of the one you are talking about, and it seems too cheap. I have the UPR and it fit great, no messing around with it. It's only a little more expensive, but a better product
So, my thoughts are:
Unlimited Performance Racing Products On-Line
and if you don't want hella loud exhaust:
Magnaflow 99-04 GT 2.5" Cat-Back Exhaust System  - $449.95
And if you want hella loud...then...either the SLPs you have listed or:
Magnaflow 99-04 GT 2.5" Magnapack Cat-back Exhaust System  - $459.85
SLP 99-04 GT/Mach 1 "Loud Mouth II" (modular) Exhaust System [M31007A] - $463.44
BTW...you can prolly find the parts cheaper in the Lethal links I gave you...
"When I know more, I'll be forthcoming. Or I won't be forthcoming, and I'll be honestly deceptive." - Les Miles