Boffin1:
I am only using the 4700mFd while I am checking it out on the Arduino board, as the onboard 3v3 supply cant handle the rush, but I scoped the cap and it hardly dips at all.
That changes things a lot. I don't think you mentioned which Arduino bd is being used,
some of them only provide 50 mA or so at 3.3V. I'm almost to the point of soldering up
my RFM22, and will see how a regular v.reg handles it. I'm using this,
I've been using the same layout and lashup with XBee Pro modules which draw 250+ mA
on transmit, and not seen any problems.