I agree with darebee.
Its been awhile since I've had to X-ray anything (my superpowers are fading with age
) but I have always been on the fast side of welding (too much caffeine w/ADDS) ) But from what I remember speed was dependent on the technique you are using for the weld. Also on what X-ray spec your using. Sounds like darebee and me use a similar technique, with the speed, but some of the senior welders, welded much slower than me and still got theirs to pass an X-ray.