Chef,
I understand everything is differant. But there are consequences of every addition that must be thought of. Adding in convoys means they have to mean something or why bother hitting them? So that means a complete reworking of the strat system, which has only recently been updated. So at this moment, CV's are the ONLY target for your submarines. As you said, they were not the main targets for submarines, yet if they were added, CVs would be the ONLY target.
So again, yes, the speed would need to be altered.
In Aces High, people don't really have patience. You have a small amount of people who do, I am one of them. Nothing better than going on a 2hr Strat bombing run in B17's (Soon to be HE111's) however most people don't. So they would expect to spawn in (Not pilot your submarine, good heavens that will take far too long) and instantly get a convoy ahead, or a CV. And then what will happen when they can't catch that CV?
The speed you posted seems far too high. Maybe for a submarine on the surface, but not submerged. Just checked Wiki (I know, I know) and the Type VII would make about 17-20 knots on the surface and 7-10 knots submerged, while the IX being 18-20 knots surfaced. These correspond with the other sources I have read.
Final point - YOU may be American, I however am a Scotsman, and proud of it. Remember, we were fighting long before the Americas were even THOUGHT of being colonised!