3 or 4 decades of travelling on mk3s means I know exactly what I'm missing - and it includes the squeaking and lurching!
Ahhh sorry lol. I was aboard a set last week, but after stepping out of a 755 regional train, the Mk3's (in standard class) seemed really dull dreary and quite dirty. First class is a lot nicer, but still, i was more pleased to have bagged a last Kings Cross to Aberdeen return trip, as the LNER Mk3's are a way superior environment in every way. And that is also a far more spectacular journey - scenery wise.
But as my sons noted a week ago, the loss of the 90's and Mk3's plus the older diesel units, takes away the traction variety from north Anglia now. It is completely Stadler land - except for the odd East Midlands 156/158.