Shock selection depends on several factors. For example, when I put Michelin "X" radial tires on my ragtop and replaced the standard shocks with Monroes designed for radials. Bias-ply tires don't require anything but the standard rated shock. If you are looking to firm up the ride of the car, an adjustable shock might be considered. Air shock are also an option but I DON"T recommend them as a substitute for good springs.
Any of the standard national brands should give good service and if you are keeping your car basically stock, a common replacement shock would be satisfactory.
The air shocks remind me of one of those Mustang legends (such as urban legend) about keeping the shocks pumped up so it would miss a couple of grade "A" wide tires sticking out (or close to) below. Seems after some time "stress cracks" formed around the top post, or stud, of the shock. Well you can guess the rest of the story. Thump, thump, zing!
Anyway, to hit the hiways and byways I go with KYB GR-2 for that smooth ride. If you needed something that will control the cornering a little better then go KYB "Gas-A-Just".
(Q) Will a "high performance" shock it make a difference?
(A) Some, if you remove an used moderately good shock to be replaced. A big difference if your car has been riding around for some time on one or more worn shock(s).
Another vote for KYB's. Not only do they provide an excellent ride, you don't have to shell out a fortune for them. Maybe a little more than the Monroes, which are also good. I think I paid about $30 a shock when I bought my last pair earlier this year.