What I have been doing is holding the drill bit in front of the screw at eye
level and trying to sight it to see if I can still see the shaft of the
screw behind it. If I can just /barely/ see it, then I know that the
screw's shaft will be a smidgeon larger than the hole it's teething into,
and that's what I'm aiming for usually.

Sounds about like my technique - except sometimes I measure the
screw's shank with a dial caliper, and grab the next smallest drill
bit from the size I measured. I'm definitely not suggesting this
level of precision is necessary - just for me, my caliper and decimal-
fraction conversion chart are easier to reach than my drill bits, and
this way I can grab the right drill bit the first time. Sometime if I
get smart I'll measure shanks on all the screw sizes I use commonly,
and write them on the screw bins, so I won't have to measure for most
of them.



1. Does pre-drilling generally create a stronger hold, because presumably
there is less wood pushed to the side of the screw? Or does the stress of
the wood split to the side add to the hold against the threads?

I don't know about this, but it sounds like the beginnings of a very
interesting experiment! I'm guessing it would depend a lot on wood
type, screw type (especially thread depth?), and probably grain
orientation. I'm looking forward to seeing more educated replies and/
or good references for this information.

Sorry I can't actually help more, but I think you're on the right
track. At least you're not alone!
Good luck,
Andy