Wait. . . or . . . Buy?

Again, I'm glad you've had better luck than I've had. But most of my AF experience has been with Rick's earlier SD1, not the M version, which I have now. If I find that the M's AF is much better than the SD1's I'll let you know.

Sure, via a T2 M42 adapter, then M42 to SD adapter.

The Tamron is an excellent lens, so lack of sharpness is not an issue. I've already done a comparison with the 70 macro vs the Tamron 90 on my NEX 7 and they're virtually the same in resolution.

Earlier I did a similar comparison using a 50mm Pentax M42 ST between the SD1M and NEX 7, but this time I was lucky enough to manual focus accurately on the SD1M to demonstrate that the SD1M was about 10%-12% higher in resolution than the NEX 7. I was just trying to do the same thing using the Tamron 90 but couldn't.

If the SD1M had the same 21 shot buffer as the SD15 I could live with the slow write times. Either large buffer or fast write time, I have to have one or the other.