I have not used a F3HP, but my F4s has a slightly smaller image due to the extra stuff it displays. It does have adjustable diopter though, which isn't important for me. The pentax 67 SLR is pretty big and bright too, but it's not a 35mm.
I can't say the same about pentax 67. I sold mine since I found it hard to focus due to dim viewfinder and bought pentax 67II which is way better.