Studio 1747, RAM and Battery Replacements

Hello Dell Community, I have a Dell Studio 1747 Laptop up and running with latest Windows 10.  I'm looking to increase the RAM as one card failed on me, as well as get a 9W battery replacement.  What's the best source for Dell parts, preferably in Canada?  I have access to my laptop's original part numbers via my service tag, which also brings to question what I should do with RAM.

My 1747 model came with Part #s Y995D and H299F, these are 4GB and 2GB 1066MHz RAM sticks.  1066 MHz is standard for RAM in the 1745, 1747 and 1749 models.  However, in the specs section of setup guide it shows 1333MHz is an option for the 1747 model only. 8GB Max compatibility,

I don't know why I didn't get the upgraded RAM at the time of new, I guess it was a listed upgrade I didn't notice.  I am assuming since it's in the setup guide, my model can support 2x4gb of 1333MHz? Will I see a big difference in performance with this jump? I currently only have one 4gb stick running as the other 2gb failed on me.

Looking for recommendations here, for where to buy and how I should setup my RAM.  Can I run a new 1333MHz stick with the old 1066MHz, or do they need to match?  Is it worth the extra MHz?