I have used both 1y and 2.5d with 4S and 6S in my heavy emaxx. The 1Y on 6S was insane, I only ran a few speed passes, it was really quick. Went back to 4S for it. Then I got the 2.5d, not too fast on 4S, 6S it opens up a lot, and is controllable. I now run a 2.5d in my Hyper ST Pro on 6S, everything runs cool (slightly warm).