IMovie Export Quality

So through a lot of online sites, I have set my IMovie(11) to export to the best quality possible, However it is still a little grainy when exported. I understand there are some codec issues in IMovie that allows this to happen, so I am not that bothered, but here is my problem.

If I export my homemade (2 minute) movie, the file size will come to 350Mb

Meaning my other homemade (40 minute) movie, will most likely come to around 5Gb

Surely there has to be a way to keep the 'Best Quality' but drop the file size amount? I mean seriously, that can't even fit on a typical DVD Disk.

Any suggestions? Thanks!