I'm new to Mac and need advice. First, is it a good idea to buy a refurbished Mac? I'm looking at the 15 in Pro. Second, I'm trying to understand the following...(1)which is better graphics; NVIDIA GeForce 9400M + 9600M GT with 256MB OR NVIDIA GeForce GT 330M graphics processor with 256MB of GDDR3 memory?....and (2) which is better 2.66GHz Intel Core 2 Duo OR 2.4GHz Intel Core i5? Thank you for the advice!!!