I need a better Smilie ... there isn't one with a big enough grin for me!!
I updated the RF60 firmware last night and have just tested it in a set-up with the V6II (on-camera Tx) and the RF60x. So 2 flashes, same channel, one on Group A and one on Group B. And yes it works perfectly, both up to the sync speed and then beyond all the way to 1/8000th. I didn't see any significant fading at the edges, so the flash coverage is excellent. Having full manual control in 1/2 or 1/3 power steps, and so easily from the V6II buttons and dial is really superb ! Plus of course flash head zoom remotely as well, which is quite handy if not essential.
After the firmware update the RF60 gains an additional menu item, which is 'AU HSS' on or off ..... this is 'Auto HSS' and is the same as the RF60x has. When set to on it is a set-it-and-forget-it thing .... it means that you can flick the shutter speed back and forwards below and above the max sync speed at will, and the flashes just keep on flashing, automatically switching themselves between normal and HSS modes .... its the same convenient mode switching functionality we have with Pentax P-TTL flashes, but via radio control rather than Optical control signals.
So the only things that the original RF60 lacks now that the newer RF60x has now is the cooling function and the AF assist, as far as I can see. Well done to Cactus for giving this extra value to RF60 owners!
Next thing to test is my Pentax AF-540FGZII with the V6 as receiver ..... firmware has been updated there also. Unfortunately there won't be any HSS or remote flash head zooming in this case, but I can hardly complain can I ? I'll still have a 3 flash remote control Manual set-up now.