Yosemite Mail 8.0 and Safari 8.0 text input slow

Since I upgraded to Yosemite I have noticed that text input in Mail 8.0 and Safari 8.0 is extremely slow. Mail, however, is somewhat worse than Safari. As I type this there is a lag before what I type appears on the screen but in Mail it can be as much as three or four seconds - so if I make a typing error, trying to backspace and correct it can be a bit of a nightmare.

As far as I can tell, it does not occur in any other application. I have read reports of Yosemite being slow but nothing seems to mention this particular problem. That said, I have tried some of the fixes such as turning off transparency but nothing has worked.

Anybody any clues?