Went back and re-read my post to see if I said anything about recoil springs without realizing it and was gratified to see that I hadn't.
Slide velocity is affected by a number of variables, the primary ones being the weight of the recoiling mass (slide/barrel combination in the case of a typical locked breech semi-auto pistol) and the muzzle momentum of the load being shot. The recoil spring must have
some effect since it exerts a force opposite the recoil momentum. Exactly how much effect it has depends on the design of the firearm the strength of the recoil spring, how much compression it's under when installed, etc.