Three thoughts: 1. With a drysuit, and an ALUMINUM cylinder, and a (floaty, positively buoyant) fabric BCD, using 30 lbs in salt water is not altogether unheard of. I was there once. But, what I found was that a) a shift to a 6lb steel backpate, b) a shift to a steel cylinder (HP120 at first), and c) optimizing my weight tended to reduce that amount to something much more manageable (12 pounds). So, go with your steel backplate AND, as you are already thinking, move to a steel cylinder. 2. I have a deluxe harness (OMS, not Dive Rite) on one of my steel plates, and I have dove a borrowed Transplate a number of times over the years. I just don't find the deluxe harnesses to be as functional as a single piece, in part because the construction really limits the positioning of the shoulder D-rings. They are not BAD, per se, they just don't offer any advantages, certainly when considering the extra expense. 3. I admit that I also like to have a should quick release (just one) when I am diving a drysuit. It just makes it easier for me to get out of my rig. So, I had a quick release sewn into a harness at my local show repair shop.
The bottom line: I can make a fully functional harness for a backplate, with some webbing and some stainless steel hardware (buckle, D-rings), and a quick release on only one side, that is more functional - for me - than a deluxe harness.
One other thought - I went down the DUI Weight and trim harness route for a while. I still have that harness, in fact, although i haven't used in in 15+ years. I didn't particularly care for it. I found it far more satisfying to get my weight optimized, and dive with a steel BP and a steel cylinder, and a manageable amount of weight on a belt.
