Short of a blower, I can't think of much you'd bolt on that would give you 5 mph.
Still a good exhaust though, and a good starting point should you want to make mods down the road. If it's in the budget I wouldn't hesitate to go for it, just don't expect big gains. Think of it as laying the foundation for future mods. Plus, it should out-last the stock manifolds by a good bit - they just looooove to rust!
Don
'01 22 Classic, 502/B1
And a bunch of other stuff
"If everything seems under control, you're just not going fast enough" - Mario Andretti