If you don't want to have to mess around with SCSI disks, consider the 630 or one of its many variants* with internal IDE (and external SCSI).The Quadra 800 introduced a higher speed SCSI bus as well as accelerated internal video. It also uses interleaved memory to squeeze out about 10% more performance.
By using faster memory and interleaving, the Quadra 800 outperformed the Quadra 950, according to the Macworld review.