$5 seems tougher

Been getting stacked in $5 HUSNGs much more than in $2 HUSNGs. I've looking through the games and it seems that my game changes mode (to worse) if I get an distinct chip advantage and my opponent doubles up back to the original stack sizes. I seem to be playing more daringly and take more chances.

One thing I am wondering is, when should I call a medium-stacks preflop all-in pushes. Let's say my opponent has 800 chips, blinds are 15/30. My opponent has been pushing a couple of times during the last hands when I have limped from the button. I get A9 on the button. I raise to 90 and my opponent pushes all-in to 800. In a recent game I ended up calling, but I was unsure wheter I just should have folded.

The pot was laying me 5 : 4 odds and I have a decend hand. However I am behind any higher ace by substantial margin, and ahead any lower ace. Against small pocket pair I am slight dog, against mid pocket pair I much worse. Only against some against some high cards I am a favorite. According to PokerStove, if he'll do this with any pair, any ace and any two face cards my equity is just over 1:1.

So in terms of looking at this situation only, calling is a +EV because of the good pot-odds. However his pushing range is the key here, if I drop some of the lowest aces hands from the set I it would be very close, and could be even -EV.

So I am still a little at loss. I wouldn't want him to double up because we would be again even. If I just fold he'll get my 90 chips and maybe I'll find myself a better hand when pushes next time ?

Current Statistics:
$2: 30 wins, 19 losses
$5: 6 wins, 10 losses