There were four racers that I consider outliers. Their swim paces at Toughman were 28, 29, 37 and 45 seconds slower per 100 yards than at Liberty. The next closest drop-off was 17 seconds. If you drop these outliers and those folks that wore wetsuits, the linear relation is quite clear.
The above graph has only the 44 non-outlier, non wetsuit swimmers. The yellow line indicates where the paces for the two races would have been equal; those dots above the yellow line indicate folks who were slower at Toughman (without a wetsuit). The blue-dashed line is the linear regression line for the scatter plot.
You can see that just about everybody was noticeably slower, and no one was substantially faster at the non-wetsuit race (Toughman). One possibility for this is that maybe the Toughman swim was set up long, or maybe the Liberty course was set up short. Both races should have been a 1.2 mile swim. These are well run races, so I don't think that was the problem. Also, the wetsuit times are telling.
The sample is small; there were only nine wetsuit swimmers at Toughman. Six of those wetsuit times were faster than Liberty (wetsuit legal), two were about equal and one was slower. This makes a lot of sense. Toughman was later in the summer, and everyone had plenty of warm weather to get in some good swim time before the race. In comparison, Liberty was in the second week of June, and a lot of places were just starting to warm up enough for open water swimming. I did a race the week before liberty and the swim was bone chilling cold.
So, what's the result? Wetsuits are faster; Duh. Everyone knows wetsuits are faster, but it's kinda fun to see some data. All this kinda assumes that most everyone used a wetsuit for the Liberty race in June. This isn't such a large stretch. Most of the folks that do two 70.3 races in a season are racers and not just finishers (present company excluded). Most racers have and use a wet suit whenever possible.
Overall, the wetsuits didn't make much of a difference in overall times. One wetsuit swimmer didn't finish the Toughman race, and another cut the bike course at the Liberty race. The other seven were pretty close to the regression line for the rest of the racers.