As the preflop raiser with decent position and a draw I probably lead for $3.5 on the flop, just to get information on what I'm up against. I play this one carefully though, since the pot is already pretty big and you only have 3 clean outs for a better hand. A check/fold is perfectly acceptable too, I think. No real reason to get involved in a big pot with such a marginal hand on a draw heavy board, unless you spike a non-spaded T.