I currently have both the 4PL and DX3R Pro, I did have the older DX3R too.

I am still using the DX3R for racing and the 4PL for rock crawling. Both are great radios and they have a very similar feel (I do not use the drop down wheel on the DX3R). Both are light but the DX is a bit lighter which I prefer for longer mains. Both controls are similar and I haven't noticed any difference in response speed (as if I could really tell the difference in milliseconds).

I found a source of DSM2 compatible receivers from Targethobby in HK for $10 each, they seen to work. Otherwise you can get SR300 receivers for about $30 - 40 and used 3100s, 3500s or 3001s for good prices too.

The Futaba receivers are $35 for the 2106 and 50 for the 2104. The main reason I got the 4PL was for its MOA programming for rock crawling. I was using a 3PKS with a Spektrum module before. The DX3R is unable to support dual ESC mixing without an external mixer.