Peter - if you are NEVER in the rain, I would hunt down some remaining RA1 inventory. You will get them cheap and they will be better than any "street" tire you will find. I picked up a set from Tirecraft a few weeks ago at a great price. Barring that, Id be looking around at DOT approved R Compounds, or the near R compound high silica tires.
If you are NEVER in the rain, you've probably had enough time on track to make the move to real rubber.
Just make sure that once the tread is worn down (65% or so left), that you're NEVER caught away from home in the rain. The stuff that happens on the drive home will give you nightmares for months.