Your other concerns deserve some discussion. I hope other members will respond. Anyway, I'll take a stab at it:
1) Lag time. Sorry, I'm not a gamer. But both my LG and my Sharp have a "Game Mode" that supposedly turns off extra processing that might contribute to lag. Dunno how effective it is, but lots of people do play games on big LED/LCDs. Perhaps some games would be more prone to lag than others?
2) Audio sync. I've never had that problem. I don't use the TV speakers, preferring to take optical out from TV and run it through an AVR to my surround speakers. Blu-Ray audio is routed direct to the AVR. If you can swing even a modest surround system, I think you'll find it's worthwhile.
3) Artifacts. I'd split that into two things: SD (standard definition) content and bitrate starvation. With the former, of course you'll more easily see flaws when playing low resolution stuff on a big TV. Similarly for the latter, when playing highly compressed cable content or streaming. Most often that means "posterization". Blu-Rays will look fine, so long as you don't get ridiculously close to the screen.
4) Edge-Lit vs Full Array. Okay, edge-lit allows for a very thin TV, which is nice for wall-mounting. (Though the audio will be poor as a result). It's also generally cheaper. The very best-regarded LED/LCDs have full array (Sharp Elite and Sony HX9xx), but also local dimming. The number of dimming zones is important. To be really effective, the more dimming zones the better, which gets expensive.
Note that the Sharp 80LE632U is full-array, but AFAIK, it has no local dimming, and if it does, I'd bet it doesn't have enough dimming zones to matter. It may have better uniformity than an edge-lit set, but I see from reviews that some think that it is also somewhat prone to color bleed. Maybe someone else can comment on that, as I dunno.
I can say that with my two edge-lit sets, you can clearly see non-uniformity when on an inactive input. (The Sharp less so than the LG). With normal viewing it's pretty much undetectable. Two exceptions:
- When using the TV as a monitor, as I'm doing right now, you may see slight non-uniformity when the page has large solid color areas, particularly white areas.
- When viewing dark content in a dark room. Like the last chapter of Zero Dark Thirty. You have to be looking for it though. My wife, for instance, can't see what I'm talking about.
There you go, and remember, the above are just my opinions. Again, good luck.