plus the 9600 is an additional component which can conk out!!!! just like the 8600

.thse GPUs generate a lot of heat and more heat generally means a higher chance of failure of the hardware components..at least this is what did the 8600 in...the worst part is...the heat might screw the logic board too...i dnt know how the 9600 is...but u never know...
If you are not doin much of 'pro' stuff (like heavy video editing) or if u r not a gamer...go for the top end 13...its much more portable than the 15...it can handle the odd graphic intensive task...and invest the money u saved into a nice external screen...