-the b-revision has MUCH better blacks. i'm not sure if there's any other improvement, but imo, there doesn't need to be, that's significant enough on it's own!
-it has NO screen filter. if you want superb ambient light viewing, the f8500 is what you want. there's a reason ppl are paying the extra money for it, and the amazing screen filter is certainly a big part of that.
-i'm not very familiar with the specifics of the LG line-up, but from what i've seen, NONE of them have good blacks. even the a-rev f5300 should have deeper blacks than the lg
-what you see in the store can be very misleading. there's a dozen things that could be causing that, and it's just too hard to even start guessing. it could be as simple as the sharpness control, or as devious as one display being fed a lower resolution. for the most part, resolution is resolution. i would not worry about one 1080p display being significantly 'clearer' than another. almost assuredly what you saw was the result of some setting being different.
-you have to remember that for the most part led's are rated relative to other led's. it sounds great, but i've heard it many times before and i'm just tired of getting fooled by it. unless you can see it with your own eyes, i wouldn't trust it. there's bound to be some major uniformity issues, or the blacks will become much brighter as soon as there's content on screen, and you'll still have to deal with all the other issues that plague lcd technology(if they bother you).
in the end, i still feel better recommending the samsung, BUT, if you've already seen it, and you're certain you can't deal with the reflections(can't tilt the screen down slightly to reduce them, or carefully position to avoid them), and you don't want to step up to the f8500, then i'd say say the lg plasma is a much better option, even with the brighter blacks.
Displays: Samsung PN64F8500/JVC X35
AVR: Pioneer VSX-1018AH, 5.1 audio
Sources: HTPC(Mediabrowser), PS3, XBOX360, Wii, Sony DVP-CX995V
Control: Harmony One