44-deg water? Cool, but not intolerable in a 2x7mm wetsuit, especially if you keep moving.
Some tips...
Don't try to do this dive straight off the boat. Get in and moving a bit. Two reasons, first warm muscles are much more responsive (and having your circulation up a bit means more 02 in your blood, so you'll feel less strain from the breath-holding). Second, the shock of going into cold water tends to cause you to exhale (don't know why, just know its's true). Moving around a bit first gives the water inside your suit a chance to warm up.
A 2x7mm wetsuit has about 10lbs of positive bouyancy at the surface (at least for me. 5'8" male, reasonably fit). I'm guessing it'll probably be down to about 3-5 lbs at 30'. Drysuits I have no clue about.
Because you're not going to be breathing compressed air to counteract water pressure, your body will also compress slightly. For me, I go through about a 2 lb change (from +.5 to -1.5) over the first 15', and guess I'd probably get another 1 lb off the next 15'.
So you're looking at a total swing of close to 8 lb from surface to depth.
As for how much weight, it depends on where you want to be neutral. If you're neutral at the surface, it'll be easier to get down to depth, but harder to stop at 30' and make the swim to the surface. If you're neutral at depth, then the swim down will be harder, but it'll be easier to not overshoot the mark by too much, and the swim up will be nice and easy.
If it was me doing it, I'd go for neutral or even
slightly negative at the surface. This makes for a nice easy descent, so when I get to depth, I'd still feel like I had a lot of 02 in my lungs.
This is largely psychological though. I have to work hard to get myself back to the surface, but that's what I'm going to want to do anyways, rather than having to work hard to take myself away from the surface, which would tend to make me want to give up only part-way down.
You're going to be descending a lot faster than you probably do normally, so be prepared to clear your ears quickly and often. Also because you're not breathing compressed air it'll probably be necessary to clear them at shallower depths than you're used to.
In general, practice swimming lengths underwater... 30' deep means 60' of swimming, which is most of a length of most pools. Also find the deepest pool you can (most pools with 10m diving platforms are 15-18' deep) and spend time just sitting on the bottom of the deep end, or fetching one of the 10lb diving bricks (or your weight belt) from the bottom. All told figure this will take at least 5-10 sec for the descent, 5 to stop and turn around, and 10-20 sec for the ascent. So you're looking at holding your breath for up to 35 sec.
Jamie