I'm 6-2 and when I'm jumping around all over my sled zig and zagging through the steep & deep I like my hand it tight and the bar riser approx at 4" where I still feel I have the most leverage and control. When I'm up any higher the geometry of the sled feels completed different.
Who knows, I may end up putting the 8 inch risers back on. We'll see how it works out once the snow flies.
My sled had 6 inch risers when I bought it and they were too short. I then went to 8 inch and they were better, but I was still hunched over a bit. They still seemed somewhat awkward. It was manageable, but I still felt that a couple more inches would be better.
I'm hoping that the 10 inch risers will allow me to stand upright with a slight bend in my arms. But it may end up being too much of a good thing. Time will tell.