Take care not to upset your gearing by choosing a tire that's wildly different from the stock tire's circumference. I am running 195/60-15, which was stock on early 240 turbos (and hence absolutely immune to any kind of fitment or clearance issues), and I'm pleased with the handling... they are adequate for the job, they respond quickly (esp. with ipd sway bars) and steering effort is close to stock. Gearing is around 5% lower than stock, which is fine. I have no intention of switching sizes, I'm very happy with this size despite the fact that it's pretty small by modern standards.

205/60 should give you approx. zero speedometer error. Bigger than that, you've got the side effect of taller gearing so your speedo will read low. 205/65 may also contact the rear fender wells on a lowered (or heavily loaded) car so they may require a bit of fender lip rollback work...

All I'm saying is, the car was designed around some really small tires, and you don't have to go particularly big to make a huge improvement to your handling. Try to get the circumference about right, and check rear fender lip clearance before you finalize the purchase.