The place where I bought it has a SP3 i3 64g for the price of the $599 S3 model so I'm torn on which way I want to go.
You'll have to weigh up your usage needs carefully on that one. If you are after a production machine, i'd personally go for the SP3 for the bigger screen, speed, SSD, kickstand (pen is included in price). However the tradeoff is that it does have a fan which when given a reason to kick up, it pretty darn loud imo, and it is also much larger than the S3. I have both and while i originally thought the SP3 fine as a tablet, once i got the S3 i realised just how big the SP3 is. For tablet use, the S3 is brilliant (although i would love for the SP3 kickstand on it). Because of the micro sd slot and usb 3.0 port, the size of the onboard storage has never really been that much of an issue for me and i'm sure i could get away with 64gb (especially now i have a 1tb usb hdd)
You've a tough choice to make. I don't envy you.