http://uboatarchive.net/Manual/Manual.htm
Check out page 17 & 18. The speeds for the given engine telegraph and RPMs are on page 14.
Unfortunately, the the to reciprocal heading data for submerged isn't available, but I think the rest kinda helps drawing a good mental picture of what a VIIC can do.
Turning a small circle doesn't mean much if it takes nearly 3 minutes to turn 180 degrees.