2012 mbp 13 high end vs low end 2012 mbp 15

[Itzmemark]

I just bought the 13 because I figured it was the "best" bang for my buck with that being said I would like to use iMovie for my gopro videos I played with it yesterday handled a 15min clip no problem. here is the thing when I start uploading my 30 to 45min clips back to back and choping those up will I need the quad core? I know in theory it will be faster but how much so. Also what will the video card really do for me since I do not play games I watch movies and "hobby" with my gopro videos. Thank you in advanced. Also as far as the ram I am aware that I would need to add some to the 15 since its only 4gb.