Dan, since you are intrigued by the possibility of using alternative lenses the SL66 might well be the better choice for you after all. For me, I'm happy to use the standard OEM lenses so it's not an issue. I would mention that the first of my 2 SL66's (both were very early production, non-metered bodies) had to be serviced to correct a stuck focusing rack (in the fully extended position - naturally, while I was out hiking with the camera in a photo backpack!). Sent it to Harry Fleenor (Oceanside Camera in CA) and all was well from the on. I believe the focus mechanism in the Rollei is known to be a somewhat sensitive area so have it checked out.
A few interesting little SL66 mechanical details come to mind, by the way... very nice _sound_ when firing the camera (distinctive klunk sound... if you pay attention to that sort of thing)... the winding crank operates like the Rollei TLRs - wind forward, then back to arm (Hasselblad is single direction). And, when the film has run out the magazine winding knob pops out and has a nice ratcheting noise and feel when rotated, quite different from the Hasselblad. Oh, and there's the really nice machined, knurled edges to that knob and others on the body... nice stuff! I love my Hasselblads but if you go the SL66 route you will not be disappointed!