Hey Ian,
Other than kayaking drysuits the only suit I have tried is the OR. I like the idea of the cheaper, no frills, Heat suit OR is offering, however it looks like it only comes with ankle gaskets and built in socks are a must for me, so I would go with the Soul.
I don't see the advantage of a neoprene drysuit unless you are spending most of your session swimming! The breathable shell material is light and lends very well to mobility and layering.
I would advise against getting a kayak specific drysuit as the waist section is designed to cinch down over a neoprene skirt so there will be excess material under your harness even if you remove the straps and plastic clips.
If you are living in a cold climate I think it is worth investing the extra money to get the best possible suit for your intended use. I did a video review of the soul here:
viewtopic.php?f=7&t=2385506