Thanks for the responses. You folks have given me some very detailed info.
I recognize that the 5.5" iP6 isn't a foregone conclusion at this point, but I'm holding out hope that it will be announced AND released at the same time as the 4.7" version. If it's not, I will likely pick the N4.
Since I use my phone for so many things besides, well, the phone, I need a device that will allow me to review/revise docs, surf the interwebz, text and email, read e-books, watch the occasional movie, work within a calendaring system, etc. in a more comfortable environment than my iP5 permits due mostly to screen size. The pen sounds like something I would use fairly regularly, and being able to multitask while on the phone also sounds like a plus, especially since I do so many things with the phone. And I do use the phone for my modest photography needs, and frankly the iP5 hasn't wowed me in that department, though I've always blamed it on the photographer rather than the camera. I think poor lighting seems to be my biggest undoing.
On the flip side, Apple's build quality and iOS have really impressed me (it was my first iPhone), and it plays well with my iMac at home. And iMessage/FaceTime are features that I've grown accustomed to since so many colleagues, friends and family members have iPhones. I've never really had a complaint about battery life with my 5. It's probably not nearly as good as some out there, but I haven't found myself anywhere where I am unable to charge the phone when the need arises.
As far as lag goes, I'm assuming that even if the N3/4 (or other new Android devices on KK) have some small amount of it, it won't be nearly as pronounced as I had on my Droid X many years ago. It made using the phone difficult toward the end of its life cycle. And while some here have said they've noticed a little bit of lag, many state they notice no lag. Maybe it's no longer an issue on the newer Android devices.
I'm not necessarily married to the iOS ecosystem, and I'm sure I don't take advantage of it nearly as much as I could. However I really do prefer the iOS of my iPhone (smoother response, never a perceptible lag, no crashes, great apps) over the old Android OS I've used in the past. Perhaps the newer iterations have closed the gap. I'm not a jailbreaker and don't plan on being a rooter, so I am just looking for something that works right out of the box. I have no doubt that the Android OS will probably work just fine for my needs, even if it may not be appreciably better (or worse) than iOS.
Thanks again for giving me so much info. I'm excited to see what the September announcements have in store for us consumers.