Need an expert to check my logic on this:

I'll just use some round numbers...

Fully Loaded 550i
Cost of car: $80K
Money Factor (3 yr lease): 2.79 from dealer - not sure why this is so much higher than what is listed on the "Ask A Dealer link", which is 2.25
Mileage 10k/yr (I work from home) - gives residual at 61%

I ran a comparison in Excel looking at where I'd I'd be at 3 years:

Scenarios:

I. Lease and invest the 80K, figuring payments of $1300 each month out of it, and an investment return on the balance at 5% (which may be high based on the current trend - long term expectations don't apply).

2. Buy outright, sell at 3 years.

Results:

1. At the end of the lease, my 86K (price + tax), would be worth 49K - putting 9K of MSDs down leaves me at $51K - so the MSD thing looks worth it.

2 At the end of ownership, my car would be worth 45-50K if I sold it - I think getting 50K would be really tough since many of the options that ran up the price might not appeal to everyone.

So it looks like a lease could be better if I am doing the calculations correctly - IF:

a) I don't want the car after 3 years (high residual makes it not so good a deal to buy out).
b) investment returns do a lot better than the average for this year so far
c) the value of the car at 3 years is actually less than the residual, otherwise the lease is a wash with more risk/unknowns.

Am I missing anything?