What about Main sheet tension? It can be the forgotten factor, if these are boats you used to point with, perhaps the more powerfull sail is stopping you from pulling in the main as hard

I know my mainsheet loads are very high, (often pull the last bit in with my foot), but they can only be achieved, by depowering the sail. I couldn't possibly pull the main in as hard as I do, which gives plenty of leech tension, with out depowering first I would just blow over.

Generally with the Irwin sail I only use the power down wind, flatten the sail upwind. In the pictured conditions, it looks like you have more power than you need. Different crew weights make a difference, but the basis is the same, flatten sail to the point where you are not overpowered in the average conditions upwind and then sail up to spill a bit in the stronger patches (only dump sheet if you have to)and down in the lulls to keep hull flying and maximum speed.

Remember most of your height comes from keeping the speed on, but you should allways have some of the windward tell tales starting to break and continualy touching it up until it slows down, then back down again. This should be a smooth process although it doesn't sound it here, when you get the feel you actualy adjust before there is any real change in speed, you can just feel the pressure change in the rig.

Hope that helps