The F-15C has better engines than the
F-15A. Maybe that is the cause for
the discrepancy.

I think its like this:

A- 25,000 lbs each
C,E- 29,000 lbs each

Nope. Only some of the E's have the IPE (PW-229). The remainder as well as
all the A's through D's have PW-220s or PW-220Es (except for the C/D's at
Langley, Eglin, and Tyndall, and several A/B ANG units that still use the old
PW-100s).

During flight test the clean E with PW-229s easily cruised above M 1.0 at mil,
whether accelerating up to it or decelerating down to it. It is not likely the
fully loaded E can do this.