Why QRO, a QCX is designed as a QRP Tx/Rx putting out a nominal 5W  (+39dBm) hence tile of its originator QRPLabs.

If you cannt work QRP, then how will QRO help?

If QCX output is 5W which is  +39dBm
128W  is  +51dBm
1Kw is +60dBm
One receive S point is 6dBm.  

Then,  the difference between 5W and 128W,  is (51-39) = 12, divided by 6 = 2S points
The difference between 5W and 1KW,  is (60-39) = 21, divied by 6 = 3.5 S points

Perhaps there are other issues, high noise areas at receiver sites, time of day,  propagation,  antenna type, height and bearing.  

I use Elecraft K2, QRPLABS U3S, QCX 20-30-40m and QCX+20m have also owned Elecraft KX3 and K3.
All are used in QRP mode at 5W or less.

My antennas are simple deltas - dipoles - verticals with this kit,  provided the propagation time of day and conditions are favourable,  I can and have talked around the world

I also have 50W and 100W amplifiers plus other rigs with 100W+ integrated amplifiers .
These I only use mainly for  QRO contests

Dave 
MM0HVW