Re: Stick with 8.1
It'll be interesting to see, but given how long it took them to get 8.1 out to the 8x over 8.0, I think the phone will be up for its renewal before it does get Win10 (especially if it needs other prodding first to Denim).
The tech preview is also interesting (I've been following it on WP Central) as apparently it was available, then stopped being so (and seemingly to flip at least once back to available again), and the reports of how it's been going on the 8x have been many and varied (hence why it's not so clear if the 8x will get Win10 finally or not).
As it's both my only phone and my work phone (which they provided) tech preview isn't an option, if I get it, it will have to be "official OTA". But somehow I think I'll end up getting Win10 wrapped up in a nice new Nokia wrapping of some description or other in the end...