I'm running C1 4.6.3 on a Macbook Pro 2.4GHz/6Gb ram and on a Win XP Quad Core 2.8GHz/4Gb ram. I have zero issues with both machines.
Just so I can try to figure out if there is something wrong with my setup... If you trash 300 photos at one time, how long before you can do anything else with the program?
Also since you brought up tethered shooting.
I have a 5DII and it is not supported yet by C-1's own tethering. So if I run Canon's tethering software along with C1 and point to the same capture folder, here is what happens:
1. The images don't always show up in C1 as soon as I take them. Usually I have to shoot a few pictures and then some come in. Shoot a few more and some come in. I can't simply shoot a photo and then review it.
2. If the USB cable between the camera and the computer is removed, I have to close C1, plug in the camera to re-establish a connection, then restart C-1.
Due to these tethering problems, I generally use other cameras for tethered shooting.