Dual head, independently choose from same desktops?

[Ben Tilly]

I am trying to figure out what
http://www.xfce.org/index.php?page=overview&lang=en means when it says
that xfwm4 to natively support multi-head and multi-screen.  In
particular I want to see whether it will allow xfce to do what I want.
 (It well may not.)

Here is what I want.  Imagine a system with 2 identical monitors.  I
would like them to be able to independently choose virtual desktops
from the same list.  For instance if I had 4 desktops, then while
desktop 2 is up on the first monitor, I'd like to be able to look at
any of 1-4 on the second.  (Looking at desktop 2 on both would be
useless but doable.)

I know that I can have 2 X servers running, and then have independent
sets of desktops on the two monitors.  This isn't what I want because
it doesn't let a given desktop sometimes be on my right, and sometimes
on my left.  I'd like to not tie the desktop to the monitor.

I know that I can have one X server running and switch things in
tandem.  This isn't what I want either because I'll often want to
leave what I have on my left alone while I change what is on my right.

I don't currently have the two monitors set up, but expect to within a
few weeks.  I also don't currently use xfce, but would gladly switch
if it can do what I want.  (Conversely I don't want to spend time
figuring it out if it doesn't do what I want in the end.)

Thanks,
Ben

PS Why would I want such a bizarre thing?  Because I put different
projects on different virtual desktops.  But often while working on
one project I'll need to refer to stuff from another, and I can't
predict what combination of things I'll want to look at.  Right now I
handle this by switching desktops back and forth, but it would be much
nicer to just have an arbitrary combination of them up to look at.