I had a pair of nRF4s with PCB antennas working perfectly at 110 metres outdoors. They probably would have had a longer range but after that distance I could not see to tell if they were working (poorly designed test 
)
I would be very surprised if they won't work very well over the range of 40 feet. And you could always try the high power version with the external antenna.
Have a look at this Simple nRF24L01+ Tutorial
...R