Tim, the HU examples were an over the top example of the concept im attempting to explain.
Potting into a limped field is certainly no slow play, id actually call that playing fast, it gives you enough information about where you stand, you should be wary of re-raises and welcome any calls.
I certainly wouldnt be happy if i played this hand the way you advocate and get no callers, I WANT someone to pay over the odds to chase that straight, betting 200 here would be incorrect, but betting 4-600 is ideal. Unless you get you opposition to pay over the odds for their draws you wont make money playing poker. The amount you win opposed to the amount you lose makes the difference.
Now there is also another few things about your bet that make me feel uncomfortable.
You bet in 1,200 and get a caller or two, you only have 1 bet to make on the river, regardless of the turn card.
You bet in 1,200 and get check-raised by the small blind, what you do ? A 400 bet will leave you in a much better position to make a decision without committing yourself to the pot.
You bet 1,200 get called by the button and check-raised by the small blind, what do you do ?
This is the problem with playing out of position, you have very little information about where you stand in the hand, and the main reason you should only come in for raises UTG with strong cards. So K-9 is a pretty standard UTG fold, and a huge leak in your game if you think otherwise.
Oh and what Chris said
Nice thread in the end of the day tho, and something you should fix fairly rapid.