Started off loose and tightened as blinds increased isn't a solid player in my book.

I definitely raise here. Do you think OPP has you beat very often? Do you think he traps? Do you think he reraises preflop with air? Those are the questions I ask when considering whether to make it 400 or push.

Most of the time I answer no to all three, and make it 400. If he pushes, I fold. If he calls and checks the flop, I bet. If he calls and bets the flop, I might push or I might fold, depending on what I think it means and what exactly the flop looks like.