This response is probably the closest to how I'd handle this situation.
Well, swimming into the current is useless. I've done a similiar dive on C-58 in Cancun, where there always seems to be a ripping current. The regulator is the easiest, simply protect the purge valve. The first option to get back to the mooring line would be to stay as tight to the boat as possible, pulling oneself along by hand, thereby conserving air. If it were evident that plan A wouldn't get me where I needed to be, I'd shelter along the wreck until I got to the highest point and begin ascending. The dsmb is a problem because if deployed too soon, it will act as a sail and carry me further away from the dive boat. I also don't see it as a viable ascent line in current because it is too fine to hang on to. In Cancun the ascent line was an 1 1/2" rope that we flapped off of like a flag. I'd wait to deploy the dsmb until my safety stop, knowing that we have a smart captain that will come to pick me up if I stay calm and float with my rig on the surface.
Here is a new scenario for consideration.
What if the current picked up during a dive and you were unable to return to the anchor line?
Loosely based on a dive on the Spiegal Grove in the Keys.
Max depth of the site to the sand ~140'
Structure near the middle ~65'
Max depth of your dive 90', current dive time 16 minutes, 1800 psi remaining
Boat anchored at the bow during slack current. You were near the stern, approximately 500' from the anchor line when current picked up. The current is strong enough that facing directly into it causes the purge on your reg to free flow. You don't have enough air, or NDL time remaining to fight your way back to the anchor line at depth. If you ascend shallower to conserve air, you're going to get blown off the wreck. You have a DSMB and a 100' reel.
How would you handle this situation and what considerations would you take into account.
You still have a fair amount of time and gas remaining. Even on PADI tables you're still 5 minutes from being required to make a safety stop. I'd attempt to make my way towards the bow of the boat, using the structure as much as possible for shelter while keeping an eye on NDL and gas.
The tallest part of most ships tends to be in the middle, so once I reached that point I'd evaluate whether the remaining gas and time is sufficient for me to make my way to the anchor line on the bow. Keeping into consideration that once you pass the middle portion of the structure, you're going to have much less cover from the current than you did on the back half of the boat.
From the higher structure in the middle of the boat, your bag has a better chance of having enough scope to reach the surface. I'd deploy the marker from the highest point I could reach, whether it's structure, or an alternate mooring line. If the bag failed to hit the surface, then I'd make a quick ascent until it did to give the boat the best chance at spotting it, then once it surfaced I'd continue with a normal ascent.
If the bag did hit the surface from depth, I'd hold my position as long as gas and time allowed so that the boat had more time to spot it and get everyone else on board so they could come pick me up.
Other considerations:
Surface currents can run counter to bottom currents. Keep a look out for your boat and make note of the direction it's pointing. That will tell you how the current at the surface is running. In a best case scenario, the surface current will be running the opposite direction. That will give you the opportunity to ride the surface current back to the boat without much effort.
Second best scenario, it will be running the same direction as the bottom current and the boat will let out some extra current line from the back. They may also be able to let out some anchor line and close the distance between you without having to unhook.
Worst case is if the surface current is running at an angle to the bottom current. Depending on the angle it could severely complicate recovery unless the boat is able to leave the mooring.
Things to know before you dive:
Depth of the site so you can plan to have adequate line. I almost always carry a reel with 400' of line and a large SMB on all boat dives now. A 150' spool is the minimum I'll carry.
What normal and extreme conditions are.
Does the boat carry binoculars?
What is the boats lost diver recovery procedures?
When I dive wrecks, if we splash with no current, my tendency is to angle away from the mooring line on descent towards the farthest point of the wreck. That way I can explore that area and make my way back to the mooring with the most possible gas. As I get closer to the mooring I'll ascend to save on NDL and gas and spend time puttering around and checking stuff out near the line.
Having a jon line can also be useful as you can use it to tether your buddy to you, you can use it to tether yourself to the mooring line and you can use it to tether yourself to the tag (current) line. Fighting current and hanging on a line can tire you out quickly and the added strain on joints can put you at higher risk for DCS.
A whistle and signalling mirror are also part of my OW dive kit. On more advanced dives, I may also add an additional spool and another SMB.