If all you'll do is open Word docs all day, stick with 5400RPM. It's cheap and easy to replace cheaply should the need arise. If you'll edit video, or do a lot of Camera RAW or high-end Photoshopping, get the 7200RPM. Just remember to put the original drive in if you have problems while it's under warranty and you decided to upgrade it yourself.
Seconded to above.
But if you have some leftover money and willingly to throw that to 7200rpm drive, by all mean do that
As example i got 7200rpm one and friend of mind have the 5400, when we do photo editing together, I can see the difference.
The heat issues is not a problem for my MBP nor my friend.