What and whyI've got a 110 litre Carve, essentially the same as your board.
I weigh 80kg. I sail same conditions as you, down the road (The Cold Toast).
I really love my 5.9 KA Koyote and MFC 36cm Liquid Pro on my very similar board.
1. You've already got the 7.4 so you're familiar with it.
2. You've already got a mast to fit.
3. That fin will do.
4. It's x-ply.
5. It's easy-peasy to handle for your skill level.
6. It's fast.
7. They're easy to find (email KA and see if you can't get one of last year's for cheap)
8. I think there'd be a gap if you bought a 5.3: 7.4, 6.7, 5.3. You'll use the 5.9 more I think.
RDM vs SDMI rig the Koyote on a 430 RDM, although I used to rig it on a 430 SDM. I think it actually had a better top end with the SDM, but the RDM is 100% carbon vs 30% on the SDM, so it is always favoured. PLus the boom is already set to fit it.. yada yada/lazy.
What about drop-shape? Best of both worlds. I've got one for the 7.2 Koyote and I really, really like.
KA KoyoteActually, while on the Koyote It's a fricken' powerhouse with little downhaul and very fast and slippery with a lot. Fantastic free-ride/race sail.
Masts againWhat mast is the 430? I rig my Koyotes on a NP RDM and a North Drop-shape. Both are "flex top". They rig well. Chances are the mast you have will be fine though. Just being a bit pedantic.
FinsWhile I'm blabbing on and on (2nd Macciato) get a good fin. MFC Liquid Pro I reckon. Honestly fins make such a difference and they are often overlooked as you don't see them and they are small. But the fin has more contact with the water, which is 15x more ...something than the air. And you can get a brand spanking new one for around $300. Best bang-for-buck purchase I ever made. Can make board feel completely different.
Good luck