You could tweak your OpenCL (hardware acceleration) Display settings in Preferences of Capture One, for a start. If it is set to None, enable it and vice versa.
While in the Preferences, check your preview cache settings.
Next, you may be on the save side with 16GB RAM, but how much is free when things start to slow down. Use Activity Monitor to check that.
You could also isolate the issue by opening a new session/catalog with only one or a few images.
And of course you are up to date with OS X and CO 9.