complete noob could do with some help :)

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hey guys, complete newbie to all things video editing. so i am trying to use some footage i took with a gopro in the r3 setting (1280x720 @ 50fps), and keep it at the same quality when i save the movie. what should i be saving the movie as?
there is a little = that says match project settings, but none of them are 50 or 60fps, and some of them are 1920x1080? i tried saving it as the HD 720-50p YUV in the .avi, but it turned what was about 1gb of video into 21gb of video? i then tried the 1280x720 in the XDCAM EX .MP4, which kept the file size good, but my computer wouldnt play it.
any help is appreciated, thanks
edit: i am using the vegas hd platinum 11 trial. trying a few out before i buy one. i liked the cyberlink powerdirector but it seemed to lag bad with overlayed videos, and i couldnt see an option for 50/60 fps, which seemed strange