Thanks for the reply - sorry it has taken so long to get back (some poorly timed holidays).
The EP hardware is my own design that uses the CC2500 and MSP430F249 chip. The AP is using the USB dongles from the eZ430-RF2500 evaluation board (F2274 chip and CC2500).
What I will do is pull out one of my older F2274 based dongles and get the EP running on that to see what the SNR is at the same distance.
BTW - regardless of the poor SNR, did you think that the TX failure/success rates were OK?