Really like to know how you make out with this. I have the same want - 30" x 40" prints with at least 300dpi. Better 600 or even more.

I have a new dual core MacBook pro and just added the 3rd gig of ram thinking to could help. Really didn't do all that much. Too slow to be useful.

I'm experimenting with various combinations of creating at 72 dpi 30x40, 300 dpi 16x20, then changing the image size to 300dpi 30x40 just before printing.

My Epson 9800 really doesn't like to print at anything less than 1200 dpi according to an Epson techy I know.

Photoshop seems to be able to work not too badly with this size of file and most print houses that print large canvas use at least 300 dpi. Maybe there is some combo of using Painter X at a lower res for creating the art, then finishing to off with Photoshop??? I really like the program so I hope there is a way of doing this.