Joined: Jan 2010
Posts: 9,778
Likes: 1,746
From: Northern California
Bikes: Cheltenham-Pedersen racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.
I recall the 210 and 1000 having slacker (72 versus 73 degrees) frame angles than the steeper Six-Ten. I have both 210 and 610 in the same ~58cm frame size and can feel the difference, both using 10cm stems and 27" wheels.
The 210 feels smaller because the top tube and head tube are moved rearward by .9cm relative to the BB (due to the shallower ST angle).