Last Croom ride I went to had a lower turn-out than the big turn-out of the previous month. Your guess is probably close to correct. Pace up the hills will be slower than the Tuesday night pace because even the A group can't completely ignore gravity, but still probably pretty fast, down the hills will probably be as fast as your sanity allows. I don't know how far the A group rides at Croom but it's probably at least double the distance that my legs turn to jello at.
If you're barely hanging with the A group on Tuesday night I wouldn't want to try and keep up at Croom with the added challenge of long climbs. If you're comfortable wheel-hugging those guys all the way through the park then you're much fitter than me and you'll probably be fine.