MacBook Pro 15" RevB features in addition to the Core 2 Duo CPU a Radeon X1600 Mobility with increased RAM and GPU frequencies.

It moved from 310/278 to 423/450 (GPU/memory).
The GPU inside the new MB Pro 17" has also been clocked higher than in RevA:

With 472/477 (GPU/memory), the Radeon X1600 Mobility in MB Pro 17" is now at the top of its specifications.
To display such information we used the excellent
Graphiccelerator from Thomas Perrier.
Last but not least, this information regarding increased frequency of GPU/GDDR will support the famous law: never purchase a Apple RevA hardware model.