To add to this, I will have a brand new RCD 510 for sale at the beginning of March. 
Why would you sell an RCD 510 when you have just had to pay an extra £395 for it as an option, when the RCD 310 is free and the RCD 510 is only worth £250 to sell? If I had no intention of keeping the RCD 510 I would stick with the RCD 310 and then keep it to put back in when I sell the car on.
No criticism intended, just doesnt seem logical plus I have probably jumped to the wrong conclusion 
I fully intended on having an RCD 510 but then I got carried away and bought an RNS 510 off eBay........
Had I decided to buy an RNS 510 before then I would have stuck with the RCD 310!
OK fair enough, but wont you need the RCD 510 for when you move the car on, or will you leave the RNS 510 in?
As a matter of interest how much did pay for the RNS 510, much cheaper than from the dealer I bet?
99% I'll sell it privately, very unlikely I will part ex, in which case I will sell it with the RNS as it will be a few years old by then and it should make the car more desirable. If I did decide to part ex and RNS510's were still worth a decent amount, I would probably buy an RCD 310 or RCD 510 and fit that.
The RNS was £600 delivered, version H (which is the same as version F - the latest version - but with V8 Western Europe maps as standard). Manuf 2 months before I bought it. Not bad!
