Why dont you consider arcsaber 8dx? Shaft is rated extra stiff by yonex but in reality it is not that stiff. Its about as stiff as victor mx70. Its a good racket if you use alot of wrist and your swing speed is fast. Net play is excellent with it. Quick enough for defence too. Z slash leans towards head heaviness whereas arc 10 is probably head heavier and less stiff version of 8dx i heard. F9 is mid stiff only. Dont know much about lyd but it didnt feel as balanced as 8dx.
I'm currently using VTZF and it is an awesome attacking racket. At first when I first get in touch with the racket, my shots are terrible and most of my shots are only 3 quarter of the court. I cant even generate the power people use to describe here. But after a few days of game, it surprised me. it is indeed a good racket but it takes time to adjust to it. Since I play mostly double, hence I go for a 4U. I have tried 3U but the maneuverability is not there. In doubles, smashing is not the only factor, instead you have to consider your speed. Anyway, in terms of power between 3U and 4U isn't very big difference. Well, overall it's still your own preference. I'm just sharing my story with u.. Good luck, bud!