While there are T exceptions, like those mentioned, I think generally speaking the spread is about two full grades. Attempting to put together any of the mainstream E sets in ex is roughly as tough as a T206 set in nm. E sets in ex/mt across the board are extremely tough.
The apples and oranges part of the equation is that many E sets are of course much smaller than the T206 set. This does not always equate with easier. With enough money and a little patience, anybody could probably put together 98% of the T206 set in NM or better within about five years. Many E sets are just impossible in NM or better.
JimB