You definately want to use the reflex clamp, even with the vacuum. the difference is noticible. Images will push forward out of the sound field and the imaging will tighten up. There is an indentation in the middle of the Sota platters, approximately the diameter of the record label, that leaves a slight gap between the record and platter. You wouldn't think with the vaccuum that this would allow much resonance, but apparently it leaves enough that the clamp is a very worthwhile item to have.
One word of caution about the clamp though: If you have a cartridge with a wide body where the width of the cartridge actually overhangs the record label when riding in the final groove the cartridge will bounce off the clamp in the deadwax. My AT-OC9 does this. It does make you jump out of the chair in a hurry at the end of the record.
One word of caution about the clamp though: If you have a cartridge with a wide body where the width of the cartridge actually overhangs the record label when riding in the final groove the cartridge will bounce off the clamp in the deadwax. My AT-OC9 does this. It does make you jump out of the chair in a hurry at the end of the record.