When you see the lap times published at a VMX meeting, there's remarkably little difference between the eras - far less than most people would expect.
The only real gap is Pre-75 to Evo, but if the track is smooth then even that gap is smaller than you would expect.
Personally, I go about as fast around an MX track on virtually any bike - while certain bikes do some things better its all swings and roundabouts. My talent and my balls limit my speed more than the bike does. That makes me slow on a modern, but reasonably quick on a Pre-78.
The reality is that we seperate eras for reasons other than their actual speed. Those reasons apply equally to Pre-95 vs moderns.