Just found an old XP table. So let's say I was on a level 84, the amount of experience required to reach the next level would be 4,582,500 in 5.3 based on the table.
Logging on any of my 84 characters, the required amount is now 506,000
Holy shit.
This seems to also have been smoothed out. Before each level since Cataclysm has often had a huge increase of required experience per level. Often in the millions. 85-86 required 13,000,000 while 86-87 required 15,000,000 and 87-88, 18,000,000. Right now my 87 requires 550,000, which is barely over what my characters at 84 require.
On the other side, I have noticed what seems to be an overall reduction in quest experience. Many that used to give 30-40k per quest now give 13-14k. Considering we dropped from 15 MILLION required down to only 550k, you still see a huge speed increase in leveling. I might actually play my alts again.