Couple things for ya. Bottoming resistance and damping are two separate things. The "oil lock" is not damping, but the air gap compressing all the way and keeping you from moving in the stroke. If you were to change nothing else but the oil level you would be able to push the forks further in the stroke. This is why we run very low oil levels, to help eliminate the air gap and then control stroke/bottoming with spring rate and preload.
If those springs are stock they should be plenty to get what you need to do. I would highly suggest adding a couple turns of preload and see how that feels. This will help with your prolong braking and keeping it off the bottom of the stroke.
And as to rebound, I suspect you're feeling the bleed and not the stack itself. With such a high oil level in there you may not be able to generate enough force to really feel what the front end is doing. Also be careful when "tuning in the pits". You can never generate forces like on the road/track, so I would go more off what the bike feels like while riding vs what the bike does in your garage. Good luck!
Again thanks man, very helpful!
As for rebound i see what you mean entirely. The old Dave Moss 'bounce' on the bike treatment is one thing but as you say no way you can replicate the forces of some bumps and heavy braking at speed.
I'm sure the springs must be fine too. In fact i've been surprised that at my 175 i've even been able to get good sag numbers after reading so much about them being pretty hard springs. But my sag seems pretty good within the middle of their preload range.
Interesting with the oil lock stuff and about the small air gap i've used. I'd been reading some stuff like this - Peter Verdone Designs - Oil Locks
I was under the impression most stock forks have this mechanical oil lock piece to support undersprung stock forks from bottoming under any extreme circumstance. I can see for guys like yourself doing a lot of track/race use it's best to get rid of this altogether, but maybe a good little extra insurance on my crappy, bumpy UK roads.
But nevertheless interesting to know i'm not using a low oil level by any means - far from it.
Just fitted some 16/40 sprockets (which in part help just cancel out the bigger 55 tyre) and a 112 chain to get the axle a little closer to the back, so need to get out and just do some serious miles.
Thanks for the help.