Tip dive in powder is something I've never totally understood. I had awful tip drive problems with Dynastar Mythic Riders, the second any pow was approaching low angle they'd pitch me over the handlebars. My old Atomic SL12s were also horrible for tip dive but I pretty much expected this given they are probably the least suited pow ski going! Interestingly I ended up with the wrong skis for the conditions and had to ski my Atomic Race SL Ti in boot deep pow and amazingly I had zero tip dive issues, I could even put weight on the tips and despite their 165 length and stiffness they just wouldn't submarine.
Given this strange set of results what exactly about a ski causes tip dive? After the Mythics I am always very hesitant getting new skis for use on anything more than on piste for fear I'll end up being plagued with mine hunting tips in powder.