Hi Rick,
Skimming through the specifications of the new Yam digital piano P70, which has the same hammer action as YPG-625, I noticed it weights 13kg (~29lbs). I don't expect the 625 to be more than few lbs heavier.
Basically, If you liked to know what the YPG-625 hammer action would be about you should try a P70.
Turning back to your main question
Using the RS to control the 300, wouldn't you basically have one of the new $750 Yamaha YPG-625's
Here's what I think: You'd get a different key action, different sound set, different styles, 625 seems lightweight and easy to carry around. On the other hand, 625 lacks storage media and MIDI connectors but, in exchange, comes with а nice wooden stand. I listed the differences, the most important being first according to my point of view. Other people would list them in different order. Basically, if you went for a DGX-300 & RS controller only the 32 notes polyphony and 88 keys would remain.
I don't say that the 300 and RS would be a bad set-up. You may not like the hammer action of the 625 and, like I said in my previous post, the difference in sound quality may not be significant. On the other hand I'd prefer having both a light and a hammer action keyboards.
I wouldn't worry about the NAMM feedback. In a big room full of 100W speakers, the 625 is going to sound pale.
What if the 625 was amplified through 200W speakers?

I hope I helped you a bit. I am curious to know what you will decide. If I were you I'd wait till june and try the new keyboard. It is only one month away.
Regards,
George
[This message has been edited by George V (edited 04-22-2006).]