Help w/ questions on my proposed setup - db651 vs. mm651 - plus 8" sub

Hey everybody. First post.

I've got questions regarding my setup for my new 2006 Toyota Tundra Double Cab. Here's what I'm leaning toward currently getting to replace the stock system:

JVC Arsenal KD-A735BT Head Unit
Alpine MRP-F300 4x50W Amp (for speakers)
Rockford Fosgate P300-1 1x150W Amp (for sub)
Polk db651 or mm651 6.5" Speakers
Polk db840 or mm840 8" Sub

The only item above I currently own is the Alpine MRP-F300.

I listen to classic rock and hard rock mainly... with some blues thrown in.

My main question is what is the difference between the db651 and the mm651? Which speaker sounds better and how? How do they differ and how are they similar? Is the mm651 worth the extra money for the benefit you get? I don't want to pay for the mm651 just because they are a higher end model if I would get just as good of results with the db651. I have the same questions about the db840 vs. mm840 8" subs.

Thanks for any help you can give! Please let me know if you have any other suggestions or tweaks I should consider.

Drew