Not a simple problem. Just to kick off the conversation, the way I see it...

Find max(x).
Find all rows where x = max(x)
Of these, find the row which has the max(y).

For your data, this will be...
3995 6427

Find max(y).
Find all rows where y = max(y)
Of these, find the row which has the max(x).

For your data, this will be...
2925 9077

The rectangle you want will have vertices that will be the four permutations (or is that combinations ) of these...
3995 9077
2925 9077
3995 6427
2925 6427

I think the points within this range are easily determined using a sumproduct formula.

Finding the location of the first max(x) is easy. If the data are in A,B,C...

=MATCH(MAX(B:B),B:B,0) which will return 3 (the row where the first instance of 3995)

Now, how do we find the other maxima, if any? Once we figure that out, the rest should fall in place.