This really is a bit of a moot point on the M8 anyways. Most of the phones were sold new in 2014. This would mean that the batteries in them have about 50% of their original life left. Unless you wanted to blow $100-150 to send it in to have a new battery put in by HTC, these things are left with a minimal shelf life at this point anyways.
I love the idea of going to an 830, but honestly, it's a 3 year old phone at this point as well. The fact that you can grab a used one for $65 or less and grab a new battery for $30, makes it a pretty good value overall. Unfortunately, for most M8 users, Verizon has never had a decent follow up. The best and most recent WinPhone's for VZW were the M8 and the Icon... There was no 95x or 15xx series that hit the largest US carrier, so you're stuck going with one of those two - or pulling and going to another carrier with an unlocked 950, 950 XL or an X3...
Anyways, sorry to see it go. I understand completely, but its still sad to see it happen. Good luck with the 830 and hopefully something happens soon to where MS brings Win10 to the forefront again. Otherwise, we'll see you when you downgrade to Android or iOS!