I'm probably not the person to say this, but I think I see a pattern here. Know what I think may be a big factor in how well a gun shoots with whatever ammunition, be it top-of-the-line stuff or $5/box stuff?
Confidence.
Establishing confidence in your given setup to put a bullet where you want it to go may take rounds that cost 50 cents every time you pull the trigger, or rounds that cost 10 cents every time you pull the trigger. Along the same note, it may require a Calfee rifle or a beat-up CMP rifle to shoot X's. Facts are facts and that means quality equipment simply shoots better (something I am learning the hard way) and talk is cheap (X's speak), but I'm thinking confidence has alot to do with it.
Because I can, I'm working on rounding up as much $5-$10 boxes of ammunition I can to have a good day of 50-yard, 5-round group testing. At the end of the day, I should have some no-bull results for my rifle. I've been shooting Wolf Match with decent results (and holding onto a few boxes from a hell of a lot), but experimenting won't hurt.