It's not the direct answer you're looking for, but on the first watt home page, they list all the reviews. I found 6moons reviews go into quite a bit of depth on each model. That gives you a feel for the different sound characteristics, as well as acknowledging the limited repair parts (held at First Watt for future service) for the SIT3 models.
A random gotcha is that the F7 has a very low amp impedance, so many tube preamps aren't a good match.
I was in the same boat as your recently, and just went thru many reviews one leisurely afternoon.