The Keystorm and America are awesome shipwrecks. I have done them numerous times and have never found the current very swift.
As mentioned for the Keystorm, you just follow the line down to the wreck. If the current is a little hard to swim against the entire length of the wreck, we have been advised by our captain to go hand over hand on the wreck. You just drift back to the line and back up to your boat. Just take notice and remember which of the two lines you came down, as the surface current can be swift if you try to swim to your boat from the wrong line, and you really don't want to do that. The Keystorm is up to 120 feet deep and has sometimes almost no current and sometimes a mild to medium current, and that is why it is an advanced dive.
The America is in the shipping channel, and should be treated as an overhead environment for that reason. You do not want to surface anywhere except the line and you need to watch/listen for boat traffic, particularly freighters. The America was blasting the shipping channel and sank when it accidentally blew itself up, and that's why parts of it are scattered. Again, you just follow the line to the bits and pieces, and follow the anchor chain to the wreck, which is quite nice. I have never experienced much current at this site. It is considered an advanced dive because of the depth and somewhat dangerous location considering boat traffic.
The visibility in the St Lawrence can be 100 feet, but this summer, with all the rain, the vis has only been about 30 - 40 feet, depending on the area. There is no thermocline and the bottom temp in the summer is in the mid-70's. The current on your U.S. side seems to be nothing compared to what we get on the Canadian side, like the Daryaw and the Lillie Parsons, which are sometimes impossible to kick against and can rip your mask off if you look the wrong way. There are lines or chains to pull yourself along these wrecks, and then you drift back. Those are definitely for not only advanced divers but very experienced divers, due to the extreme currents and depth.
Our Canadian boats go through your U.S. customs by Boldt Castle and we always love to visit the Keystorm, America and Vickery. If you are an advanced, comfortable, experienced diver, then those dives should be appropriate.
Hope that helps in making your decision.