Ah whattheheck... based on the OP's original rating system:
ANH: 7
ESB: 7
ROTJ: 6
TPM: 3
AOTC: 2
ROTS: 4
The OT can be scaled up by one point (if you stop thinking about "other great movies"), the PT one point down (I was being nice to it for the parts I liked).
That would certainly represent the gap better.