I think this match between Tilden and Vines gives a better view of what they were capable of. Vines creates a net point that looks not out of place in modern tennis.
The last serve of the match seems to be of considerable pace and also a serve by Tilden about 1/2 way through the video seems to be very heavy (Vines returned it out).
Tilden is the one with the rolled up sleeves and Vines is the one with a short sleeve shirt.
Recommend you go to full screen.