You won't get your Str8 as sharp as a disposable and a disposable won't be as sharp as a Str8 either!! They are 2 different animals and IMHO shouldn't be put up against each other. Your looking for a smooth keen edge that will take in 3 pass's all your beard down far enough to feel nothing but smooth skin when you pass your hand up and down your face after your shave.
That to me is Str8 sharp!!!