If you are so keen on the 'physical separation' then perhaps a WM that includes some synthetic black bars to give defined visual separation of tiles?
You didn't specify what resolutions your monitors are running. Out of curiosity, what are they?
For about half a year now, I've been using a 3-display setup centered around a large iMac. While the iMac display is nice, I kind of miss my old work flow. The iMac resolution is quite awkward, actually, because it's too small to split in two or four separate work areas, but at the same time it's way too big for just one window. There is really no good way to use that screen efficiently. So I often end up splitting it into two overlapping halves with a code window and some other window, but on the whole the setup is not as satisfying as the 6-screen.
I've now got my 2011 22" iMac sitting next to two 22" Dell UltraSharps, and it's amazing for my workflow :)
That said, I also do a heap of work on my 11" (1366x768) HP notebook, so I'm crazy, and use so very many virtual desktops its not even funny.
On the road with 2 LG 23" monitors (6.5 lbs each) and a Dell M4700 laptop. i3 WM provides the tiling needs. Love the setup, not too much context switching (i.e. changing virtual desktops) and sufficient screen real estate to do my work.
Do you use virtual desktops as well?
I have been using this for 3+ years now, and while people always look at me like I'm crazy when setting up 6-7 monitors on my desk (I freelance so I usually lug them around or just buy a used set of monitors for a few bucks), I could never go back. Not switching windows, and using your peripheral vision for things like database load, or just plain having 2 editor monitors and 2 reference browsers open at the same time is invaluable.
While I can work on a single monitor, even a huge one (I love the 3k x 2k notebook resolutions), I feel cramped because I don't have the physical separation that comes from the multiple monitors.