Deadlift Form in Regard to Physiology

As a competitive strongman it’s basically a staple to have a strong deadlift. I come to you guys today concerned about my TERRIBLE speed off the floor. I have pulled 500, and it seems like even a 315 warm up is somewhat slow off the floor, but once it hits my knees it flies up. I’m 5’9", 230lbs, short arms with very NOT flexible hamstrings (lol).

Basically, I’m bending down pretty far to get to the bar; when I pulled my 485 for a double, I had a VERY close foot stance and fairly close hand placement in hopes that this would make up for my incompetent body structure. However, I’m starting to think I’d be more advantageous for me if I chose a more wider stance with my feet and my hand placement as it’d allow me to get more posterior chain work into the lift instead of a close stance demanding my lower and upper back.
What do you guys think would be the best stance for somebody like me?

Are there any other assistance exercises that train the lift off the floor other than deficit deads?

deadlifts
135x5
225x3
315x3
365x2
405x1
440x1
485x2, tried a third rep, just not 100% yet!

SLDL’s on 3-4 inch defecit
135x8
225x8
275x8
325x8
drop set
225x8

hip thrusts w/ axle
123x10
213x10,10,10 gut check on all of them!

GHR’s
x8,8, calling it, hamstrings feeling fried/crampy

you can try doing speed pulls and even use bands or chains to force you to be faster. or even try dimel deads and swings.