Oh boy, here it comes again... (this question is getting a bit old)
Unless you want to be able to charge 8S instead of 6S batteries per channel, the DX6 is more than enough. Or you could go with the older, larger 406 Duo (or its slightly revamped newest cousin, the 456 Duo - the latter apparently coming at a much higher price than the DX6, though... the 456 currently offered for 400€ here while a DX6 is only 280€... question is, do you plan on charging beyond 30A often enough to make it worth the difference? Around here most tracks / race series set charging limits much lower that that)