DaveGordon:

I wouldn't buy a Spyder without AC. Track it on a hot day and you'll find it extremely uncomfortable. The AC on mine died at Spa on a hot day and I nearly rented something else instead of driving my sauna. Will probably make it more difficult to sell, too - and all for 10kg?

+1, AC is a must have. For re-sale and as a safety feature on the track and on the way back home.