most times vs a tag I would just check that flop and try to spike top pair, unless he would call with a lot of PP only to fold on this board.
I'd only bet to mix up play so he thinks I'd bet nothing sometimes too.
As far as getting comitted or not with your bet sizing, I haven't given that much thought either, but I try to bet the size I think gets him to fold the most, whether it makes me comitted or not.
for example, say you bet 90 or something that left him with like 2/3 pot on the turn. he might call and try to showdown, but then you can shove if he checks the turn or river. maybe this is the same as other options, I dunno really, just a thought.