I would definitely want a 510/306 connector as these are my go to Attys more then a 901 plus the 510 acts as a double since the 306 threads are the same so you would have 2 of the best Attys that fit one connection, it would also be possible to have 901 threads on the outside of the 510/306 connector so even if it where a 3 in 1 if you wanted to run an 801 you would only need that one adapter 901-801 or 510-801 but the way I see it a 4-1 still would be extra nice