David,
It depends. For flattening a tabletop glued up from 4" boards that cup a little ( say 1/16" irregularity ) I'd probably use a few quick sweeps with a belt sander across the grain ( I expect some flak for that ) and check with a good quality straightedge, followed by the RO150.
Planing is another option, but in my experience it's not that easy to plane cupped boards to flat, the plane tends to tip "into-the-cups" and it's easy to take off more than is necessary. I love handtools ( especially handplanes and chisels ) but experience has showed me my own limitations.....
A planer like the EHL 65 is an option for heavily cupped boards, but it's rather tricky, be it superfast. Run it along the grain and take off minute amounts per pass.......
A decent straightedge of sufficient length is probably your most important tool. Once within the 1/64" mark, the RS2 E will most likely shine.
I don't think the differences between the RS2 E and the RS200 EQ are large - the Plug-It powercord comes to mind, but other than that?
Regards,
Job