Sounds like you've made up your mind then! You've seemed pretty stressed about your IPP well before this announcement.
I don' know if I will be able to read the letters on the 9.7" screen comfortably if I have two pdf open side by side.
Based on experience with the Galaxy Note Pro 12.2, that size is about right for holding. 12.9" is a bit large. Not sure about 9.7" and 10.5".
If we know when the iPad PRO 12.9" will be released, the decision making would be easier. Certainly September/October is too far. If it will be released in June, I just wait and decide.