I've never used a large but I do have the x-large. I wouldnt swap it for anything. I dont really see how it can use that much more lump if youy use it correctly. I shut mine down when I'm finished and reuse the leftovers next time. Also I sometimes just move the lump to one side and put the meat on the other side for a indirect cook without the plate setter. This works great for a reverse sear. I doubt you would have room in the large to do this.
It mainly just boils don to how many people you will be cooking for. On a normal night it's just me and my wife, a lot of times my youngest son, his wife and 2 kids will come over and during holidays as many as 16 could show up. With the x-large I can cover it all.
Almost forgot. Over the holidays we smoked a 20lb fresh ham. I filled it with lump when we started and 16 hours later when it was done I still had lump left and never added any during the cook. Thats pretty good if you ask me.
X-Large Big Green Egg