Panic, by 'f/s' I take it you mean Feet per Second. Yes / no?
Yes the 'bearing speed' is the important factor there (as I understand it anyway) and lightweight is always a good thing when you're trying to rev the snot out of something.
As for if they would self cancel, probably not, but it would stand to reason it should be close in your + 10% -10% example; the error would likely be exagerated the larger the numerical change (ie +15% -15%, just for numbers).
