I own or have owned four convertibles consecutively and I'd say the most important factor in general terms would be the interior dimensions (cabin space), which puts two-seat roadsters at a disadvantage in terms of heating up quickly and to a higher temperature (both top up and down). On the plus side, they cool down the quickest with HVAC on, and the 987 HVAC is the best I've personally encountered (I have the "basic" HVAC, not the climate control).
As far as top-down driving
with the windows up, which I assume you'll be doing alot of, I still find the Box to be "hot", due to the low seating position and the aforementioned small "cabin". It wasn't till I started reading Boxster boards had I ever read about people driving top-down with the A/C on, but I do it occasionally now too, and suspect you'll want to do the same. Obviously, windows down, they're all about the same
I agree with Randall, that tinting the 987 windows isn't someplace you want to go (although I'm currently contemplating tinting my windstop).