How do I know if my irons are too whippy for me?

As Above?

I felt my 7 iron and 6 iron the same distance,
9 to 6 Irons' distance increase as per normal?

see a pro for your swing,
see a club fitter for your query on the shaft, but i believe its your swing and not your clubs.

if 7i and 6i same distance, you are probably adding loft to your club at impact. see a pro to sort that out.

Cheers and good luck!

if your club is too whippy,
most often it will "slice" your ball
or make your ball fly " fade"

take the advice of eiji

hard to say, my fade is also a result of me holding off the release of the clubhead, though in the past it used to be worse because the problem was compounded by a shaft that was too heavy for me.

eiji's advice is good (to me) because it takes the guesswork out of the game, especially when you are facing problems -- build a sound swing around equipment that is suited for you, and within your physical limits