JohnnyT wrote:
[...] you need to remember in ELO that the difference between 2500
and 2800 is vast, and the difference between 2800 and ~ 3100 is as
vast. It is not 10% better, it is closer to think of it as TWICE as
good. Or more likely to win MOST of the time. It is a HUGE
difference.

Specifically, an Elo-rating gap of 300 points (and it's the difference
that's significant so, yes, 2800 vs 3100 gives the same results as
2500 vs 2800, gives the same results as 1100-1400) corresponds to the
stronger player being expected to score roughly 85%. The approximate
values are tabulated below, by approximating the real data on FIDE's
website[1].

Rating diff. Score
----------------------
600 99%
500 96%
400 92%
300 85%
250 81%
200 76%
150 70%
100 64%
75 60%
50 57%
25 54%


Dave.

[1] http://www.fide.com/official/handbook.asp?level=B0210
Beware that the table is rather hard to read as the columns are
too narrow. The expected score is to the left of the rating
difference in each case.

--
David Richerby Poetic Toy (TM): it's like a fun
www.chiark.greenend.org.uk/~davidr/ child's toy but it's in verse!