Hi!

>> Anyone who has used either or both machines: could you comment, and
>> recommend one over the other? The 650 is likely to be quicker than the
>> 700, from all I've gathered, is this a sound assumption?

Some additional information, based on NewerTech's GURU and my experience
with both models:

Both run NetBSD well, although my Q700 hangs when you move the mouse
during boot before the ADB probe (seems to be a known problem).
The Q700 needs four equal-size 30-pin simms; the larger ones may be hard
to get these days. The Q650 can take one 72pin simm at a time (fastpage
PS/2, 80ns or faster), but does memory interleaving when pairs of equal
simms are installed (makes it about 10 % faster, according to Apple).
The 700 has a somewhat weird graphics card, it supports 256 colors, or
millions of colors if you have all 6 VRAM slots filled; the Q650 takes
only two VRAM simms, but can do thousands of colors and more resolutions.
More convenient if you want to run color X
Speed difference is not dramatic (25 and 33 MHz, both can be overclocked
a bit using a clock clip); there's also the Centris650, which is almost
a Quadra650, but runs at 25 MHz.
The 650 has space for a CDROM drive, which can be used for a second hard
disk.
Both have an AAUI 10Mbits ethernet port.

Hope this helps. Whichever machine you take, have fun with it!

Best wishes,
              Nico
-- 
Dr. N.J.R. van Eikema Hommes   Computer-Chemie-Centrum
hommes@chemie.uni-erlangen.de  Universitaet Erlangen-Nuernberg
Phone:   +49-(0)9131-8526532   Naegelsbachstrasse 25
FAX:     +49-(0)9131-8526565   D-91052 Erlangen, Germany