I dove the Spiegel Grove and the Duane in July. I can't say that I have any specific advice, except to tell you about my dives.
The Spiegel Grove was great. The current was enough that I wanted stay in the lee or close to the deck. I did have to make one longer swim against the current to get back to the line. I was really sucking wind. If I had my druthers, I would have descended to the deck (slightly protected) to make this trek, but my insta-buddy was on air, and close enough to his NDL that staying up higher was wise. If you have a Nitrox cert, use it. If not, consider getting it. NDL of air is the limiting factor on this dive for most people.
I don't normally wear gloves, but for these dives it was smart. I did not want to spend lots of money on expensive gloves that are rarely used, so I bought some semi-disposable Gorilla Gloves from Lowes. They are thin stretchy lycra material, with the palms and fingers dipped in flexible rubber. They offer moderate protection, are cool and comfortable, and very cheap. For me, they prevented some fire-coral burns and scratches.
We penetrated the Spiegel Grove though several different entrances. The depth of penetration was short, there was always a visible exit and ambient light, but there was lots to see. A good strong flashlight makes it much more enjoyable. Being of the first few to penetrate is better, since some people (me included) can't help but stir up the silt a little. I tried to be very careful and slowly frog kick and coast as much as possible, but I was far from perfect.
About the Duane: I have no idea how often this happens, and no idea how willing the Captain is to repeat this method. Maybe it is a common occurrence. During our ride out to the Duane, the Capt heard from other boats that the current on the Duane was strong and everyone was choosing alternative sites. He elected to investigate anyway. After arrival, it was decided to dive anyway. I was told that the decision was based on the following:
1. There were no other dive boats at the site, and the Capt could choose any line/buoy, and maneuver as needed.
2. There was a good DM/diver ratio.
3. All the divers had been deemed to be of sufficient competence, as observed by the DMs on previous days/dives.
Everyone was advised to be ready for a quick entry and descent (like some drift dives I've done). Messing around with missing cameras or mask straps would not be helpful. We were all ready and seated like a line of paratroopers ready for a drop. The Captain and crew tied the stern (yes stern) to the up-current buoy. We all went in rather quickly, and started down the line to make space for more above us. The current was the strongest I've seen (but I'm not very worldly). I felt like a wind-sock, at the mercy of the elements. But, by the time we reached the Duane, it was more mild and manageable.
The time on the Duane was excellent. The visibility was very good. The line we descended was on the Duane's bow. There was a huge grouper at the bottom of the bow that could only be seen by doing a DeCaprio over the gunwale. Then, in small groups, we explored the wreck from bow to stern, going back and forth from port to starboard many times. I don't remember the penetrations as well as the Spiegel, but we did go inside many times. We only had to stay even (hover) with the current occasionally, usually just swam enough to slow our drift.
The timing was perfect, as many of us reached the stern at 1/3 tank, and ready to ascent the stern line. When we broke the surface, we found the dive boat with a granny line waiting, moored with it's bow to the buoy. Carefully sliding the granny line the stern was easy and getting back aboard was reasonably effortless.
It was really cool that the Capt could move the dive boat to the down-current buoy for us. It was sort of a Boat-Drift-Wreck dive! If there had been others at the site, it would not have worked, since the down-current buoy would likely have been occupied.
I was one of the first to complete my safety stop, so I ascended a few feet and snapped this photo of the gaggle of divers below me.
