Upload & Sell: On
I tried the 2x II on my version 1 (when I still owned one) and the hit in IQ was substantial enough that I didn't ever use it. I don't believe I had a particularly outstanding copy of the 70-200, and I was never happy with any extenders on it. The 70-200 II, however, is a completely different story, and in combination with the 2x III is well-known already as being surprisingly stellar...this in spite of the fact that I understand the extenders to be designed largely for use with the supertelephoto primes...
I recommend borrowing or renting one before purchase; a comparably small cost to see for herself...