Here in Calif. I use 2 different wetsuits:

3/2 (3mm torso; 2mm limbs) full suit for ocean sailing and a 2mm shorty (short sleeve, to mid-thigh) for summer mountain lake sailing. I use my 3/2 for surfing also, but that gets chilly in a hurry anywhere north of Santa Cruz. A 4/3 suit would definitely be too cumbersome for sailing. If you're going to be in conditions cold enough for that thickness (doubt it in SoCal), it's time to check out drysuits. Dive suits probable will be too thick and may not have flexibility panels where you need them. I'd stick to surf shops and sailing shops when looking.

I also use booties at all times that have a split toe design. These keep the tootsies toastie and provide good grip when out in the trap. There're not as bulky as boots, so I like the feel much better. You might also consider a gor-tex spray top to go over your wetsuit when the air temp. is cold also.