If there were to be 2 classes why does the split have to be 583 and 675/620,why not 583/675 and 620.
To make the 675's competative would cost well over £700 and (for something that nobody can quantify for definate,remember the BB saga) and for that money you can drop in a 620 lump.
For what its worth i voted for 1 class ,the same as this year.
Butch