Will I see a massive performance hit?? 2.5Ghz i5, one 8GB Crucial RAM module one stock Apple 2GB module...total RAM reported by System 10GB.....but Erhm a gard it's mismatched.........does it REALLY matter that much??????
Performance hit ? Nothing that you will notice.... What you might encounter are (fatal) errors and the OS crashing (worst case, mind you). If that happens, just pull the 2gb stick and live with 8gb instead of 10gb. You won't notice a difference.