Ouch, well, no $3500 projector can be perfect, and this may be the biggest problem the HD7100 has. Rated 32db noise level (full power?), doesn't sound to bad, but it is a bit loud in full power compared to most. It is definitely noisier than the H78. It's much better in Low Power mode, but still above average.
I don't think any but the most critical will be sufficiently unhappy with the levels at low power, to pass on the HD7100, but I imagine a few people will. In high power mode, the fan is going to be noticeable - not terrible, and no problem for TV/sports type viewing, but I find it, for example to be a bit louder than our central air conditioning in my "great room" viewing room, and I notice the air when it comes on with my own projector.
So, the bottom line, is that the audible noise is probably the only aspect of performance that can stand some improvement. If both were 4-6 db quieter, everyone would be more than happy, including the most critical. Alas!