Sean,
I prefer the 9000PRO, for many reasons. But then I could be biased. The honeymoon with my 9000PRO is still going strong (over a year now). Both the SD1 and 9000PRO are great instruments. Here in Australia they are about the same price before the deals.
For me the polyphony 126 Vs 64 for the SD1 was a big point. Also the lay-out and the user interface of each. For me I prefer the 9000PRO's keyboard action (it is so close in weight to my piano's action).

Also, The fact that you can have three instruments layered in the right (R1,R2,R3) as well as the left(L) and be able to set three separate split points - for the accomp., left and R1/R2, and also R3 gives you a lot of flexability in performing. The sounds and the styles - this is very personal - upto the indevidual's own taste. Both instruments are soooo strong in this area unless your ear takes a definate like or dislike to either, then I would say that the sounds wont be the deciding factor. The combination of your most sought after bells and whistles will become the deciding factor.

On the styles, I nearly always end up tweaking the 9000PRO's styles. Whether its the choice of instruments or the tonal qualities of the instruments. That's another strength of the 9000PRO - the capability of the almost un-ending number of options for varying a style's sound and character. I think that is why Yamaha engineers set such a bland middle of the road setting for the styles. They know that the indevidual will want to change the mood or the sound of the style to suit what ever the occasion is.

I guess Sean if you have zeroed in on both of these instruments, my advice is to really spend a lot of time with each before making the decision. This includes spending a lot of time going through the user manuals - both are available from the respective web sites.

Also, if you can do the evaluations through the same sound system. If you can't manage the same sound system then get a really top quality pair of head-phones and use them. I used this technique and I believe it paid the dividend. I spent a lot of time on the 9000PRO before I finally bought one.
Lots of luck Sean. Try not to become impatient during your evaluation trials - enjoy the experiance!
Jon.