I'd start the X11 on 49mm/rev. I am not sure how much you know about these timing-on-the-fly speedos, so sorry for teaching you to suck eggs when I say...
The ratio will give you the all round driveablility. If it's too high (in the 50s) then the motor will get hot and the car will be lethargic all round the track. If it's too low (in the mid-40s) then the car will be quick out of corners, and quick to reach top speed with a cool motor.
The boost rate will control the acceleration, but you can't feed it too much too soon, otherwise it will get hot. If you feel a higher ratio is what you need, then feed in the boost rate slower (400+), but if you go for a lower ratio to suit a twisty track, then feed in the boost at a faster rate (400-).
Once you find a balance for your local track, it will be easy to make small changes for other tracks. Always (ALWAYS!!) check you changes against the clock, never against a temperature guage. Temp gauges are there to make sure you don't make a silly mistake, not to find out how fast you are! Whatever you try, write it down, write down the fastest lap, and write down the difference between your fastest lap and your average lap. A fast qualifying time will be when the difference between the two is less than 0.3s.
Hope that helps!
