I'll answer a couple of those for you... the other's I'll have to check into.
If you want to "customize" one, you're probably going to need to order it online, which you said was not an option, so that's a no go.
The 9600M will handily lay the smack down on your old 6800GT. You'll be happy with it. It's one of the faster mobile GPUs.
Of course, if you really are into gaming, and can wait, there's an MSI (GT725) that's on Amazon on pre-order for $1350 that has a Mobility Radeon HD4850 which will lay the smack down on any (single) mobile GPU that exists.
I would say that Best Buy is going to be your Best Bet (pun intended) when it comes to retail stores for laptops. Most other computer retailers are going out of business, mostly because they have crappy prices compared to Best Buy. However, if you can find a going out of business sale, you might want to check into that.
Good brands for laptops:
Acer, Asus, Gateway, HP, MSI
(Sony, Toshiba, etc. are decent, but generally overpriced)