We were there last December over 4 nights. The first day the high was only about 60, the second day around 70, and the third day around 75.
On the first day, we basically had SAB to ourselves (except the lifegaurds, who outnumbered us about 10:1 and, I think, thought we were nuts). Once we got in the water, it seriouisly wasn't that bad, but we're from upstate NY. The hot tubs were divine. About the only aspect that was unpleasant was getting out of the water (for example, the long walk from the pool to the waterslide was a bit
and not for the faint of heart).
On the second day, there were probably about 50-60 people in the pool area. It was a fair bit more comfortable but you still found yourself more inclined to hit the hot tub than the pool and getting out was still slightly chilly.
On the third day, there were probably at least 200 people in the pool area. Overall, it seemed pretty comfortable and this included getting out. But I was still inclined to spend more time in the hot tub than the pool.