This is not an easy question to answer. 30 tears ago it would be easy. There was one technology and that was it. So then, thickness was the only real variable. Now you have such things like seals and other things. I splerged and got a Harvey's suit with wrist and leg seals. I cook in it. unless i am in the 60's water, the 3mm farmer john is too much. old style suits it would be probably a 6mm or better and 10 on the core. I asked when i bought it about its equvilancy thermal protection. What i got was that a 3mm is about the same as a standard 5-7mm suit. The suit does not keep you warm, it stops heat loss, sounds like double talk but, with the seals, you have no water circulating and hence no heat being flushed out. The less suit the better. Less suit compression, and thus less weighting issues. Another thing you can try is a lavacore. Its a wonderful technology. 0 weighting issues. Each technology has its costs. And remember you just cant pick a suit and disregard whe is needed by the rest of your gear. Ie you just cant change from a wet suit to a lavacore. you will sink like a rock untill you comp for it. I tried my lavacore with a bp/w and a lp120 on and i could barely stay on the surface ansd had roll problems till i changed to a lighter plate and even that did not help much. lavacore with al tanks in fresh water ok steel tanks in salt water ok, but normally you need some lift from your suit to comp for the gear weight in fresh water, and provide for a bubble above you to keep you belly down. No wing lift ... no leverage to keep tank on top.
