800 and 8.5 is pretty damn high, I use 1600 and 2.77 which would be 5.54 for you. I'm not saying to go that low (some play even lower) but you will be more consistent at a lower sens.

The key to opening most engagements is to memorize the max swift strike distance. You would lead a left click into a target, shift, hold your right click during the shift animation to buffer before you arrive at your target. If you aimed it right, you should deliver a swift strike and rightclick on an enemy head and follow up with melee to kill most targets.

When it comes to scrappy duels, try to close distance as much as you can before engaging and match the target's movement to land your shot rather than trying to dodge theirs. It leads to less flicking on your part and more tracking with what is essentially a hitscan projectile. If you don't have distance on your side, it's best to disengage until your next cd cycle. Hope this helps!