FormerlyHemlock
Hero
So 1,100 might not be "deadly" deadly, but a full 1,800 would be deadly deadly deadly and spam with a side of deadly. If I had to guess I'd say 1,500 is probably the practical upward limit of total survivability without a short rest, and even then I think the remaining 2,000 before a long rest would have to be sliced pretty thinly.
It depends very much on the details of your party and their tactics. I had a party of 3rd and 4th level characters win an encounter against 1280 XP each (6400 between 5 characters; 3200 base XP x2 for quantity) using nothing more complicated than terrain, a Web spell, and the Sharpshooter feat. It was great excitement and very memorable, but it actually ended up not being that much of a resource drain and I bet they could have done it again. (They didn't need to, though, since they'd already met their objective during the first fight and could scram.)
Perhaps you mean to say that 1800 would be deadly, deadly, deadly only for the particular party that you're running the game for, but in the general case of 5th level PCs, I think there exist parties who are capable of handling way more than 1800 XP worth of foe per encounter.
-Max