I have a 3,5 F with Planar lens and an older Tessar RolleiFlex as well--I've only used the Tessar model a few times as in couple of rolls of film and its nowhere near the optical quality of my Planar 3,5 (especially Wide Open and yes I know the Tessar design will result in the image sharper when stopped down) but then maybe the Tessars vary a bit as I'm not that familiar with the T models. As for the 2,8 versus 3,5 Planar I honestly can't say and I have both BUT my favorite is again the 3,5 version. It is the best RolleiFlex model(that I own) as far as I'm concerned but then I have a Maxwell Split Image focus screen installed on that one and WOW-What a pleasure to use compared to the old dark screens.