I too have been searching for a tent for rafting that is also big enough to stand up in. So far I've discovered that no matter how much you spend on a big standing height tent you will always have to guy out the rainfly in windy conditions. We have a large Browning ( Greystone 4 Grey/Gold
) that we picked up for cheap and it held up awesomely in high winds up in Buena Vista, CO at the end of March and in the morning it was noticeably cooler outside of the tent but not what I would consider warm compared to a smaller tent with a shorter height. We have camped with 3 adult people multiple times and it never feels crowded (until someone snores), it has huge screens so even though it's nylon it's still cool - the fly is also sort of a light grey reflective color so that probably helps it in the cooling dept.
We camped in the rain last year in it and stayed completely dry and were able to make breakfast in comfort. The floor is heavy material and held up to a cot without a pad under it without tearing the floor. If the fly is on you can dress in privacy while standing up which is really, really nice when you're used to backpacking tents.
The downside of tall tents:
IF you don't guy down the fly because the ground is too hard where you are camping or you don't think it will be stormy and a storm blows up your poles will break. You have to guy out in wind, period, or you will soon be the proud owner of a deflated tent.
The search continues...