Great question. The difference between the Pro-Godess and the Slipstream is that the Pro-Godess short is a board short that has a sewn in neoprene short that is fitted to your legs on the inside. This short offers warmth and a little extra padding up against your outfitting because of the full length neoprene short inside. How we make it is by taking the Aphrodite short and sewing the Lunch Box Short into it to put it simply.
The Slipsteam on the other hand is a regular board short that a has a stretch of neoprene that runs from the middle out side of the leg, up, across the upper area of the bum then back down the other side of the short. The neoprene has been placed in those areas because when you are sitting in your boat that is the spot you need the stretch the most making it a very comfortable light weight short that will stretch in the legs and the bum to prevent riding down.
If your split between the 2 the main difference is that the Pro-Goddess is going offer you more warmth because of the full neoprene liner and the Slipstream will be a lighter weight short perfect for long hot summer days.
Hope this helps!