One question about Labyrinth Lord since I've only been able to glance over PDF so far, not much has changed, right? Does it essentially have all the same information as the RC?
Not exactly. The Rules Cyclopedia collects everything from the 1983 Basic and Expert Sets, the 1984 Companion Set, and the 1985 Masters Set. It's a very complete game system meant for playing a campaign from 1st to 36th level. It has rules for general skills, weapon mastery, building strongholds, ruling dominions, and conducting mass battles, all missing from LL; plus many more high level monsters and magic items, and far more detailed rules for making magic items. And the rules for paladins, druids, and mystic monks!
Labyrinth Lord merely emulates the 1981 Basic Expert Sets, which describes the game rules from 1st to 14th level, and then assumes a rather unstructured and open-ended advancement after that. So Labyrinth Lord and the Rules Cyclopedia are compatible, but once the players reach the 15th level of experience, you'll want to switch to using the RC. And you might have to tweak things to make the experience, thief ability, and spell progression tables line up (I just use the RC tables throughout the campaign).
Where are things different between Labyrinth Lord and the old Basic/Expert Game? The changes are minor, but they're there (Dan had to change a few things for copyright purposes). The XP tables are slightly different for all the classes (but that's not very important, and easily ignored). Labyrinth Lord includes 7th, 8th, and 9th level spells, where the Expert set only went up to 6th level spells. But the spell lists in Labyrinth Lord are a little different from the Cyclopedia, because LL had to take all its spells from System Reference Document, in order to be OGL compliant! Also, the RC included the druidic spells from the Companion and Masters sets; LL, of course, does not.
Finally, clerics have two oddball changes in LL. First of all, LL clerics start casting spells at 1st level rather than 2nd level (Dan has said many times that this was a change he made intentionally to make the cleric more playable, and if you want to do things the old way, just bump the cleric's spell progression back by one level). Second, the turning undead table, instead of following the old 11/9/7/T/D pattern, is extended to 11/9/7/5/3/T/D, meaning that clerics must be much higher level before they automatically turn or destroy undead. (I happen to really like this particular change, because it means that low-level undead can challenge a party longer. This is one case where I happily substitute the LL rule for the D&D rule in my campaigns.)
I'm sure there are a few other differences, but they don't leap immediately to mind.