Sub-$500 for LoL and video

[dredsilver]

I'm currently looking at two laptops that both have labor day sales: Toshiba Satellite (http/www.toshibadirect.com/td/b2c/cdetland.to?poid=2000037648) and lenovo Z575 (http/www.newegg.com/Product/Product.aspx?Item=N82E16834246322).
I've come down to these two based on affordability and the A-Series, which I'm hoping will meet my gaming needs at a low cost. I'm essentially looking to be able to smoothly watch video and play League of Legends. My other usage will be pretty slim on the laptop: OpenOffice, web browsing, etc.
The Toshiba is Trinity architecture with a faster quad core and better video (7640M) but the lenovo currently has a $100 MiR and free upgrade to Windows 8 (not necessarily a pro).
The Toshiba will effectively be $90 more after rebate. My other option is to get the A6-4400M instead of the quad in the Toshiba. This will set the price difference to $50.
I'm attracted to the Toshiba for it's current architecture and better proc speeds and integrated GPU, but the final price after rebate on the lenovo is holding me from pulling the trigger.
Sorry for the wall of text, but I ask of Tom's, will the dual-core A6-4400M meet my mobile needs and be powerful? Or should I get a quad core model in the lenovo or A8-4500M Toshiba?
(Also, RAM difference not important; will be upgrading myself to 8gb regardless)

 

[bak0n]

The A6 or above will do well for LoL at lower quality and resolution settings. LoL doesn't care for machines running around the 2ghz level or less unless its also got a lot of graphics HP. I've got 10 systems of all shapes and sizes and have tried LoL on all of them.

The z575 will also be extremely slow at loading which will really annoy after a while.

 

[dredsilver]

The A6 or above will do well for LoL at lower quality and resolution settings. LoL doesn't care for machines running around the 2ghz level or less unless its also got a lot of graphics HP. I've got 10 systems of all shapes and sizes and have tried LoL on all of them.

The z575 will also be extremely slow at loading which will really annoy after a while.

LoL doesn't use four cores, anyways, right?
Will I get much performance gains out of the quad for what I'll be running application wise?

 

[dredsilver]

Best answer selected by dredsilver.