I just measured the outer rolling diameter of my tyres its 1860mm.
found a nifty little program for working it all out on the net put all my info in came up with 223.6 kmh down conrod and 206.2kmh down into murrays corner.
speed calc

Thanks harry for the compliments it wasnt as bad as I expected the front end wasnt to floaty I hit the limiter before the kink down conrod then again coming down onto the chase i was only pulling 7200 in fith down onto murrays. the bob tail helped a bit through the kink could carry a lot more speed through there
I plan on fitting my 4.3:1 for next time. I dont want to go too tall or it wont pull as well out of the corners.
Apparently the track is a bit longer as they start it back a bit for the dip and also around another 100 meteres past the normal finish line.
I run 47.89 back in 2000 with a 3.3 diff the shorter track and a long way off the speed I was doing on sunday