The aTV3 preset was designed to give the best quality with the smallest file size. High quality, not being similarly designed, will give you smaller file sizes but with a resultant loss of quality. That said, whether you personally can detect that quality loss is dependent on a lot of factors, such as screen size, viewing distance, etc. So it really comes down to your personal preferences and storage limitations.
I can tell you that, for me, using the aTV3 preset, The Hurt Locker came out to 22GB and For a Few Dollars More was 18GB (both only 2h 11m long). If you simply must have a smaller file size, I would suggest using the aTV3 preset and lowering the quality setting a bit (maybe 22). Often with BR's you can get away with that with minimal quality loss.
Lots of detail (rain, grain, action, etc) or dark areas can increase the file size as the aTV3 preset will try to accurately encode every little detail...right down to the grain in the film.