Think of it this way.

If you had to lift a weight using a pulley system twice, once with a super strong chain, the second time with a flexible peice of nylon, you will have a harder time lifting it with the nylon because you "wasting" energy on stretching the nylon.

So yes, stiffer frames are faster. Assuming all things equal you will probably gain a tiny amount of performance. Not noticeable of course.

Next topic.