MM,
Sounds as if the SD1 really fits your needs. I switched from SD1 to T2, at least partially because I thought the key action would be ligher on the T2, but there isn't that much difference.
I think if I were you, and had the time, I'd wouldn't purchase the SD1 unless you could find a real steal on one. Surely the successor to it is in the pipeline and it should be even better. I hope it incorporates more of the features of the Ketron Midjay, particularly the operating system.
All that said, I'm really enjoying the Tyros 2 and finding exciting new features every time I play it, even after owning all the previous Yamahas.
DonM