That is a perfect vane for 4 fletching. I have the exact same set up on GT 55/75 Pro's and all broadheads fly awesome. I use the 75/105, but I think it is all personal preference. If you go to a higher profile vane like a Blazer or AAE Maxhunter, 4 fletching will actually inhibit your arrow flight. They will essentially catch too much wind, and try to "cross steer" the arrow from the back. These vanes are already designed with a high enough profile that they shouldn't need to be 4 fletched. The lower profile vanes like Duravanes and Vanetecs are perfect for the four fletch scenario.
I used to 4 fletch at 90 yawing FF 360's. Can't remember the offset , but I used my helical clamp on my Bitz. Only reason I switched was when I went to FMJ I was having FOC issues with the 4 fletch and wraps. So I ditched the extra fletch and wraps. If your having doubts about if you should go 4 fletch, then do a test. Fletch up three arrows with 4 fletch, slap a BH on and do a comparison starting at 20 yards and work back.
I tested them and groups were similar but 4 fletch hit lower so in sticking with 3 fletch.
Ya I could see them hitting lower because of more drag. At least you didn't go all in and refletch all your arrows and then find out you didn't like them.