when drilling jets for that "perfect" size, yes, theres the wire guage/numbered/imperial (thou) sizes that can often be in between the metrics, or...
when soldering the jet and redrilling, bear in mind the LENGTH of hole can also control fuel flow... so by filling the jet up with more solder, which increases how long the hole is, you can fine tune a certain size hole.
ie, i go too lean on a .45, i start 4 stroking on a .5. but if i fill the jet with solder halfway then drill it at .5, its now flowing somewhere in between the two and poifect
you can also tweak mixtures with the oil ratio, and fuel level.
noone can really recomend the ideal size for you because they ARENT you!
this is what plug chops are for! you need to tune the engine in for yourself! sorry... but altitude, oil, oil ratio, fuel... it all plays a part in jetting.