yeah, trying to increase your swing speed can often lead to swinging from the top, thus releasing all clubhead speed way before the ball.
Yours arms etc will look like they are swinging fast, but in reality the clubhead (i.e. the bit that hits the ball) will be much slower.
I have been practicing with a very slow tempo lately, same back as follow through and Im hitting a 6i 160m.
If I try to speed up (incorrectly) it drops back to about 140m.
as long as you are accelerating through impact, thats all you need for a consistent hit.