I'd be very surprised if this new lens would not optically beat both of the ones you mention - they are both old designs now.
I actually have both of them, each has its good and bad points. With the f4 you lose one stop, but if this lens is anywhere as good as the recent releases for IQ (15-30, 24-70, 150-450) then - in my opinion - the IQ is worth the trade-off, as well as the reduced weight compared to the Pentax f2.8.
It's worth a try anyway!
Originally posted by xmeda You can get the older Tamron 70-200/2.8 or Sigma 70-200/2.8. Both are 1.2-1.3kg which is less than DFA*70-200/2.8 and both cost less and provide more light than DFA70-200/4.. and its rather difficult to beat 70-200/2.8 lens closed to F4 with wide open F4 lens..