I don't know that it's worth $260 to get 2 more GB of RAM and a slightly faster processor. 6GB is still pretty good, and it's not like you're going to be playing fancypants computer games or doing massive graphic design. If you can upgrade the RAM later, you can always increase longevity that way and spend the money when you feel a need (computer feels slow or needs change).
The backlit keyboard is nice to have, I really like mine and miss it when I don't have it. Slot vs. tray, not a huge difference. Battery life can matter if you go a long time between being able to plug in, but not so much if you're often near a plug.
We use Dell laptops at work, have not had many problems, but that could be luck of the draw, they are all under 2 years old. My husband has two Sager laptops, they are not a major brand but Sager/Clevo are responsible for building laptops under other names so it's kind of like going factory direct but still getting support. So far so good there.
On the Mac, I haven't had any problems with viewing powerpoint presentations with Office, but sometimes giving powerpoint presentations can be fun.
If your department/school is standardized on Windows I might not want to stray so that I don't waste time on technical support issues, though, unless you have built in technical support (self, spouse, good friend). You can run windows side by side with Mac OS on a mac, but then you have to pay for a windows license on top of it.
Good luck... computer shopping is more overwhelming than bike shopping.