Uhh other than heat and power...I guess performance and price? The GTX 460 outperforms the 465 in pretty much every aspect there is when it comes to graphics cards. The GTX 465 is generally seen as a failure and the GTX 460 is what it was supposed to be.
I only payed $180 for the gtx 465. $160 after rebate.
The 460 768M is $115AR and is faster than the 465, but if you bought it then theres not much point.
But its stupid to use an old slow and small HDD as the boot-drive, youre just slowing down your system for no reason.