I would strongly recommend you drive around a car with the windows closed and AC off for an hour. If you're happy with the experience at the end, get the comp car. As specracer noted, very little air moves through the cabin. Combine that with the fact the comp car does not have either AC or the NVH panel that separates the seat backs and rear bulkhead, and a LOT of heat comes into the cabin and stays there.
I really wanted the carbon stripe, but I consulted with many Ford GT program employees. First thing they always asked is how much you're going to use the car. Knowing that I drive quite a bit, nobody would sanction the idea. I would definitely ruin the seatbacks sweating my ass off.
Is it doable? Yes. It will be substantially less pleasant than having AC. There are people that believe it will be worth more because there are less. It's a possibility and if that's a motivating factor, go for it. But the high-end non-AC Porsches are virtually unsellable. It is beautiful though. MMs CF work is stellar.