I have a 10.5 Pro and have literally just come back from the local Curry's where I tried out a 12.9 for the first time. I love it, took all of 5 mins to adjust. Not too heavy, not too big, such a nice bigger screen. After 10 mins I didn't want to give it back and the 11 I then tried seemed like a toy. Glad I did it, totally fallen for the 12.9 now and will be ordering the 1TB on pre-order day. I'll also go for silver as the SG is a fingerprint magnet, and I just love the contrast and rawness of the silver, and I think any nicks etc will be less visible.
EDIT: To point out the "not too heavy" was also taking into account the security bolt on the back of the device, which the assistant, who owns a 12.9, said was probably most of the weight I was holding.