This is a pretty awesome problem to have but I am running out of room in my grow tent. Im running a 430W HPS in a Secret Jardin TD80. I have 3 master Kush and 1 Green Crack going right now. The GC is going perfect, staying short bushy and full of bud sites. The MK are getting pretty stretchy. My problem is that They are growing so fast that its already really cramped and im only on day 12 of flowering (wich is going great by the way I have tied some of them down to make room, but they keep shooting up long stretchy stalks as a counter. Would mild trimming be wise? Keep bending?

Keep bending like you said or I would say look into supercropping. I had to do both on my last grow to make sure all my plants fit under my 600. I don't like to trim to much during flowering, just because if I trim off healthy leaves I feel like I'm wasting perfectly good growth. But that's just me.