Normally a cascade is just too cold and too dodgy for some to work with, not to mention a little bif of danger involved.
However, a small chiller system, that could be used to chill 2 gpu's AND the freezer's condensor, and you could use a hardcore single stage gas without any real effort.
I'd say R410 or Isceon89 and you'd have a -51 to -55 baseline to work with.
Not exactly an easy task to deal with the thing, but in the end you'd have a very mild cascade that would be your waterchiller too as long as it's tuned to hold that load.
iv seen em b4 iv got a cool idea, water chilled condensor on one unit lol, the run the chiller back into the condensor of the chiller, be fairly quiet. Would that work? chiller - hx of big unit -chiller condensor-chiller
Oh yes, when your unit comes here, there will be a full run of results, and hopefully I'll have a few compressor choices as well for you by the time it's here, in case you want a little 'extra' in that unit too
To be honest I really can't wait, will be about the prettiest unit I've had the pleasure of putting my hands on
PS: The ultimate would be a mount a mach in a Mountain mods style (as in external dimensions the same as a MM case, fabricated to keep cost down) using a 3x120mm HX and a 1x120mm HX, with finned tubing and desuperheatercoil, superior anti vibration compressor mounts and use a 'proper' mountain mods case to fix ur system to it............. submit your quotes to me now