[phish]

I have a slightly different take on this. I think the decision of how many bets to put in w/ 55 should be more determined by how he plays postflop and how it will affect his post flop play. From what you've described, this is the type of guy who will be unlikely to fold any hand that can beat yours. In other words, if he has 77 and the flop comes AKJ, he is not likely fold his 77 just because you made it four bets or six bets pre-flop. On the other hand, he will keep bluffing until he meets resistance. And since 55 is a pretty vulnerable hand to overcards (or overpair), my tendency is to not make the pot too big pre-flop. This way, his bluffs will be a bigger mistake and your folds (not too often hopefully) will also be better. To illustrate:

Let's say you just call his reraise. The flop comes Q49. He'll keep coming at you, and you'll call. A 3 comes on the turn and a 4 on the river. Now you can either just call the river or even raise expecting to get paid off by an AJ. I don't really like raising with such a marginal hand before the river against such a tricky aggressive opponent because if he reraises, you have a very difficult decision. Now by not raising before the river, you're giving him a free draw if you're ahead, but since the pot isn't as large, it becomes less of a mistake.

But if the board shows KQJT all spades and you have no spades, you'll probably want to just fold and since the pot isn't as large, you would not be making as big a mistake even if you had him beat.

The point is, 55 is a vulnerable hand. Against his likely holdings, your edge is not much more than 50% going to the river. And if you're playing HU against this guy, you want to first analyze where your profit is coming from against him. And I don't think it's coming from building the pot pre-flop with such a vulnerable hand. I think your profit will come from the fact that he is so PREDICTIBLY aggressive post-flop that he'll keep betting/bluffing until he encounters resistence. With a hand like 55, I would tend to not raise too much pre-flop and let him take the lead and bluff his chips away post-flop, unless the board is really dangerous or favorable.

In general, you don't want to play passively HU. But 55 is precisely the type of hand which is medium strength (for most boards) where you are likely to be ahead but won't like it if you get reraised on the turn, since you won't have redraws and may well be beat even by another mediocre hand. Calling down w/ this hand against a predictibly aggressive opponent is probably the best course of action.
And to capitalize on his predictive aggressiveness post-flop, not building too big a pot pre-flop w/ such a vulnerable hand may be the best course of action.