I don't know if you will feel the difference below 5000rpm, but your engine will revv a lot faster. That's what I noticed with my UPR offroad X-pipe anyways.
I have a friend with an '01 Cobra with a bassani catted X, and he swears that the cats give a better torque curve, which makes sense. You will lose power below 2500rpm, but will gain power where it counts (3500+)
The bassani is a quality peice and i'm sure you will enjoy it, but you might have to take it to the dyno to see the gains. I'd say you'll gain between 8-14rwhp.
You don't think an offroad X/high flow catted X will gain 8rwhp over the stock pos?? 2.25" crimp bending, 4 restrictive cats vs. 2.5" mandrel bent, no cats or 2 high flow cats with a 7000rpm revv range....I think 8 peak HP is entirely possible if not a little under the norm.
atvcrazy: Different brands of X-pipes will give off more/less rasp. Quite a few bassani o/r owners have complained of lots of rasp with chambered mufflers. My UPR offroad X (different design) rasps a little, but I love the overall sound. Cats will mellow out the tone and tone out some of the rasp as well over offroad pipes.
You will notice the sound difference more than the power difference with a catted X, IMO. Can't say with the O/R ones, I've never had one.
On my 2001 Cobra with a catted X, catback, C&L CAI setup & steeda U/D pullies I gained a total of 32 HP over stock. I don't know how much of that was from the X pipe.