It's a good question, and since BMW has the most to lose if the Residuals are off, I'd guess yours will be worth a little more than the residual you cited since you put much less mileage on than allowed. I'm in the same boat, so I'm interested as well.
As an aside, I'm not familiar with the term "1 pay lease." Does that mean you paid your entire lease payment up front, as a down payment? If so, that may have been an extremely poor decision based on what I know about leases and could factor largely into your early buyout decision. What I have been told is that if a leased car gets totaled, your insurance goes to the leasing company and leaves you with NOTHING. No equity what so ever. There is hopefully a very low probability of totaling a car, but when you consider the possible loss, still not a good Net Present Value on that financial decision.