I am about to buy a used trash can as well, as I had several kernel panics on my old Mac Pro during the job. Could be a ram stick, could also be the graphic card or heat issues ... anyway, I have investigated this thoroughly and I tell you, don't get a 12-core. Take a 6-core or 8-core, maybe a 10-core, but these are rare. The best clockspeed to core-count performance is certainly the 8-core @3,3 GHz (not the usual 3,0GHz). It is a possible processor upgrade you can do yourself, but sometimes there are machines with exactly that a CPU offered on eBay. You will also be fine with any off the shelf 6-core or 8-core. To buy the CPU for the best possible upgrade is something like $250, so, no big investment as swapping the graphic card! That is why you should not buy any 4-core (or rather any d300 Mac Pro). And I would not advice for the 12 core, as its Logic performance is actually worse than the 6 or 8 core where it counts.