The SPT and the HTRZIII are mediocre autocross tires at best, compared to the Star Spec, Kumho XS, Bridgestone RE01R, etc. I had two sets of SPTs and a set of the HTRZIIIs on the RX-8 - they were all round and black and held the car off the ground, but they weren't that spectacular.
If it were me, I'd buy the Star Specs. Honestly, I'd be
buying a second set of Star Specs for my car, but I've decided to try out the Nitto NT05s instead. Unfortunately, Nitto doesn't make a size that would work for you.