the fastest time for horde i have seen is 5:17, alliance i have heard 4.5 hours from 90-100 single player. regular players with no knowledge will take 12+ easily
http://elvinelol.com/forums/forumdisplay.php?49-Guides has 90-100 speed leveling guides for both horde and alliance, have a browze through that if your interested. the horde guy has his run through on twitch stream archive so have a look at that also, it might be usefull

as for collection quests i leveled from 90-96 with a friend and mostly everything shared, wasn't an issue