The condenser fan wouldn't have anything to do with the fan speed of the cabin fan.My cabin fan at full speed has heaps of capacity and the A/C cools down extremely quick.I have heard in the past that the fan speed resistors in the X5 fail regularly this may possibly be the issue with the low cabin fan speed.Also just check that the condenser fan is working correctly when you turn the A/C on and off as mentioned earlier this may have something to do with the cooling of the AC.If you don't think the cond fan is working and causing the issue just run a garden hose over the cond core to cool it down and see if the temp of the AC lowers.