I agree with Dr G. I've owned a MKVI and a Serie III and they were totally different even though they both sounded like . . . . . . SOPRANOS!
We all make way too much about these things, I fear.
Plus, after reviewing the link provided by Antipodes, I will re-issue my common warning - beware of marketing hype. Reading those comparisons between the Serie II and the III, I had to laugh. The authentic differences are in the necks - one removable, one fixed, and the presence of absence of a hi-G. Big deal.
After that, all the blather about ribbing, etc., etc., is only mildly interesting to me. I'll bet that few if any readers here could play both side-by-side (or listen to any of us play them side-by-side) and tell any difference except within the normal variances experienced among all saxophones. And definitely, few if any would HEAR any difference.
Selmer isn't the only manufacturer who does this . . . read any manufacturer's material and you'd walk away thinking their horn has ALL the whizbang features to set them apart from the others.
The LAST thing I'd do before buying a new saxophone would be to read the manufacturer's drivel. You should play horns yourself, then choose one to buy. DAVE