I think you can drop an entire day's XP budget into a single encounter, but that doesn't mean you should, at least on a regular basis. As has been pointed out, it can screw with the balance between classes, especially if you have a class that can just nova (Paladin, I'm looking at you ...) and it can be really easy for a turn of dice luck to render party members dead in a hurry.
That said, you can make memorable fights by dropping Deadly+ combats on the party, and IMO they work well as climaxes to long combat-oriented story-threads. I also have to admit that I've only ever calculated XP value retroactively--looking back on a combat. At this point I just kinda trust my judgment of what the parties I'm DMing can cope with.
That said, you can make memorable fights by dropping Deadly+ combats on the party, and IMO they work well as climaxes to long combat-oriented story-threads. I also have to admit that I've only ever calculated XP value retroactively--looking back on a combat. At this point I just kinda trust my judgment of what the parties I'm DMing can cope with.