Curly:
Wetsuit. Cold water. Mostly fresh. I considered the AL80, but liked the idea of the steel tank's neutral buoyancy when empty. Haven't done any diving requiring stage bottles so far, and probably will not.
Well, do you dive with enough weight that you'd be able to wear a steel tank and still have enough ditchable to swim up?
I mean, could you, on a full tank, dive to 100 feet, deflate your BC or wing completely (simulating a catastrophic failure) and be able to swim to the surface? If you coundn't, could you ditch enough weight to swim to the surface?
If you're okay with that, could you place the weight of the tank on your back and still be trimmed properly?
The reason why AL tanks work well for wetsuit diving is the same reason that they make good stage or deco bottles - they're neutral when they're half full. That way, they're never really heavy and never really light... They "pass through neutral" as they empty.
Steel tanks don't do that. They're always negative - just moreso when they're full. This is great, assuming that this is what you want. For example, this characteristic would not be beneficial as a stage bottle... Because diving with them full would be a pain.
As back gas, steels work well, and help you to remove some of the weight off of your belt or integrated BC. They also get some of the weight off of your hips and up around your shoulders, where the most buoyant part of your body is: Your lungs.
However, depending on your circumstances, putting that weight up and back there may work badly against your trim - you may find yourself "flipping over" or "turtling" because of the weight on your back, especially if you're diving a backplate, which already moves a good bit of weight onto your back. Other things that make it worse are thick wetsuits with lots of buoyancy on the front of your body and the placement of the rest of your weight too far back on the waist.
But the worst thing that a steel tank can do is, when used in conjuncunction with other weighting options, place you in a position where you do not have enough ditchable weight. That is, for some people in some circumstances, they can not swim up their rig from depth (even if they ditch whatever ditchable weight they have) if a bladder fails catastrophically. One formula for this situation would be a heavy steel tank or two, freshwater, a thick wetsuit, and no ditchable weight. In a situation like that, a diver can really get himself into a lot of trouble. Imagine what would happen to a diver who could not swim his rig up and had a catastrophic bladder failure over a 1000 foot bottom!
For this reason, there are many divers who simply follow the creed of not diving steel tanks when wet. (A drysuit offers a redundant buoyancy source.)
...So the big picture is, yes, you may be able to dive steels while wearing a wetsuit; you might even find it desireable for the weight you get to take off of your belt. However, ensure that it does not overweight you or put you in a position of not being able to extricate yourself from a failed bladder situation.
...And even if you find that you can do that successfully, you still may find trim issues with a steel tank, especially when used in conjunction with a steel backplate or if you use double tanks.
So what's the bottom line? I recommend that if you're diving wet, you stick with AL80's. Later, if you end up getting into staged deco diving or simply want more gas, you'll end up using the AL80's as stage bottles anyway.
If you do decide to go steel while wet, I recommend talking to Genesis about it... He's been able to do it successfully and can give you some pointers on it. Also, the steels which seem to work wet in some cases are the Pressed Steel high pressure tanks such as the E7's and E8's... Not the heavier steels on the market. As great as those are, however, they do take a high pressure fill to equal the amount of gas available in a low pressure AL80; and high pressure fills are not available everywhere. You're also forced to use a DIN valve, which means you'll probably have to reconfigure your regulators. (Additional cost of about $50, usually.)
...And then you'll have to use an adapter or reconfigure your regs again to rent tanks in most places - so if you're traveling and don't want to carry your tanks with you, then you'll have to redo your regs for the yokes on rental tanks.
...Of course, none of this is really that big of a deal - I'm just pointing out why I'd recommend that you buy AL80's as your first tanks and go steel when/if you begin diving dry.
