I would go with a 650 if you want a desktop form factor or a 950 if you want a tower. The 840AV is faster and has the DSP, but is also more in demand than the 950, so they usually sell for a lot more. Failing one of those two, then the 700, 800 and 900 would be my next choices. I don't like the expansion options on the pizza boxes or even the 630 style cases even though my second most used Quadra at the moment is a Performa 631 with a real 040 installed. I prefer lots of Nubus slots in Quadras.