I used a 1 Meg on my SG's tone control in the neck to brighten the stock neck pickup (500K volume, 1 meg tone). That's the approach I'd take: First try normal 500K pots and if you feel it is lacking top end/too dark/mushy, put in a 1 meg ohm pot.
The danger is that it can sound harsh & thin on the top end. Lower rating pots aren't all bad, they do help fatten up the top end. It's mostly a matter of taste and finding what fits and most of the time that boils down to 500Kohm pots for humbuckers. For example George Lynch's guitars quite often don't feature tone knobs, but he still had some resistors soldered in to emulate the effect of having one.
