I wouldn't assume you'd get the same battery life on a MB Pro with Windows that you get with OS X. Most of the long battery life comes from some tweaking on both sides (My Asus netbook does 8 hours plus on Windows 7 but much, much less with anything else). Definitely worth checking.
I don't find the Thinkpad with the AMD chip underpowered for anything I want to do - Word 2010, Picasa and Chrome primarily.

You may want to take a look here - http://reviews.cnet.com/8301-31012_7-10431386-10355804.html