Going with a Tesla solution would actually be way way more expensive (when bought new). A Tesla K20 is 3520 gflop/s for $2900 (and then you need a server to put it in). The Mac Pro is 3500gflop/s for $4000.
The Tesla card does have a significant advantage in terms of double precision math, but that isn't the kind of workload we're doing. If we were to go with GPUs on Linux systems, the NVidia GRID card or AMD FirePro server cards are probably a better fit. Or maybe even NVidia Quadro or GTX, although they don't have the proper fan layout and there would be some tears shed over getting the power sockets cabled.
The Tesla card does have a significant advantage in terms of double precision math, but that isn't the kind of workload we're doing. If we were to go with GPUs on Linux systems, the NVidia GRID card or AMD FirePro server cards are probably a better fit. Or maybe even NVidia Quadro or GTX, although they don't have the proper fan layout and there would be some tears shed over getting the power sockets cabled.