Until WW1 cricket was very much an 'off side' game - for example, Wilfred Rhodes was considered a great mid-off and mid-off was a hugely important position. In earlier days hits to leg were considered by many to be 'indecent', even unsporting. Bowlers generally bowled a line more inclined to the off side and the keepers had a clear view. Also most slow spinners looked to turn the ball away from the right handed batsman. If you read the likes of Strudwick or Tiger Smith on the subject they basically say this.
It would appear that, in the 1920s, fashions changed and off spinbecame more popular and quicker bowlers started to cultivate swing more and more and many found inswing much easier. Never having kept I suspect that off spin/inswing is harder to take as the ball goes into a blind area until passing the batsman so, for pace bowlers, keepers might start to stand back more. I think through the 50s this happened more and more and then the view of Alan Knott held sway and keepers stood back to some very medium pace bowlers. This has altered in the last 20 years I think and a keeper standing up is much more likely
I understand the Maurice Tate's keepers always stood up to him - he was very accurate and, I suspect, bowled generally around the 80mph mark (going by descriptions of players who played against him).
With regard to speeds down the ages - Hobbs played against Ernie Jones & Tibby Cotter and would have noted if they were quicker or slower than, say, Larwood or Constantine (he considered them of similar pace, taken over time). Hammond played against Larwood and Lindwall, Cowdrey against Lindwall and Lillee. That such players don't say otherwise suggests not to much (if any) difference in pace.
Hobbs actually said the best fast bowler he ever saw was Neville Knox - who had a very short career hampered by what today sounds like stress fractures.
As has be observed here, those considered quick from the 70s (when I started watching) would still be considered fast today. Seeing film of Chris Old I would now say he generally bowled in the mid 80s, sometimes a shade quicker, rather nippier than I recall.
Re Barnes - from reading a number of players comments (Strudwick, Smith, Hobbs, Noble and others) I'd suggest, c1911/12, he bowled in the low 80s, but with great control and spin, and could put down a 'surprise' ball that was somewhat quicker.
