The T3 makes a poor master controller, unfortunately... Most arrangers are built as 'one keyboard' solutions for players. Probably the Korg's are the best in this regard.

And, in all fairness, as you already HAVE a Yamaha, I would recommend something ELSE as a second keyboard. There is too much in common between Yamaha products (or those of any other manufacturer), an overall sort of 'sound' that adding another one would not give you the range of sounds that adding something by a different manufacturer gives you.

In all fairness, although Ian loves it NOW (mind you, he didn't while he had the PSR... Ian always thinks whatever he currently has is the best possible thing!), but I don't think the FSX keybed of the Yamaha's is noticeably better or worse than any other TOTL WS's keybed. It's VERY similar to Korg keybeds, Roland keybeds (on the Fantom line), Lionstracs keybeds (from what Fran says), and many others. Even my old Triton feels VERY similar.

The only plastic that is radically different is my G70, which is a little heavier and smoother, with more full size keys.

If you can wait long enough, and save up just a bit more money than a MoXF, I'd wait until the Kronos drops. That's going to be either 61 plastic, or 76 and 88 wood (and far less than an arranger costs) and seems to up the bar in a BIG way over anything else currently out. I think, unless your needs are immediate, that waiting until we get a chance to see this in action might be the best move.