The 6+ has a much stronger/larger/beefier battery, but of course it's having to deal with larger screen display etc.
Yep, Apple Pay will be taking off and how useful and widespread it will become is anybody's guess. Apple will get something like 0.15% or $0.015 per transaction (not sure on the exact number) and it cuts out what the Banks, and CC companies collect. There are competing payment technologies out there that Walmart & Target are implementing so it's going to be interesting to see how all this will pan out for us the consumer.
Although the 6+ is larger than previous iPhones (I had iPhone 5) I find it still slips into my jeans pocket easily or in my breast pocket jacket without issues. The new location for the power button is taking me a bit to adapt to. I do love the Touch ID technology.
1st Mate who's hard of hearing tells me the sound quality is much improved with the 6+.
What I'm finding very useful is that I can make a call using my Contacts on my Mac running Yosemite OS so long as my iPhone 6+ is somewhere in the house and is on and connected to the home Wi-Fi LAN. This is a very convenient feature. This does use up air minutes, but soon Cellular companies will start introducing the ability to make calls over Wi-Fi/internet rather than using the Cellular network.
I've also changed my AT&T Family Plan to a Mobile Share Plan which saves me $30/month along with my Business 25% discount. Very niceeeee. 😉 😎