QTR-Quadtone RIP

Two questions in one post:

1) I've been printing on a Epson 2400 with QTR sending RGB files, after a B&W conversion in Photoshop, of course. Should I be converting to grayscale mode? What am I losing or gaining by sending RGB files?

2) I'm using the Ilford Smooth curves for Epson Prem Luster. Is there a better curve for this paper?

(I guess that's actually three questions.)

Thanks,
George