From my experience different driver versions have different behaviours. With 10.5 (if I remember correctly) the windows streched and maximized on both screens but with 10.4 10.6 and 10.7 it back to just maximizing on one of the screens like most people want it to. And no im not running xinerama. Hardware is HD5770 but I have also seen this change on a HD4670.
The part where it only maximizes to a single screen when running a single desktop is referred to as xinerama hints, even though xinerama isn't used anymore. (At least, that's what the nvidia twinview documentation referred to it as, since it was an option when using twinview)
I'm not sure what you mean... I'm running something similar (though with four monitors). It's all one desktop, compiz covers the whole thing, can drag 3d windows between screens, all that... what more is there?
In windows with my two HD 5870 Eyefinity 6 Mini-display port cards I can do the following with all 6 monitors connected to one of the cards:
1. Group all 6 monitors using "eyefinity" so they all act as a single monitor. This doesn't seem to be an option in the amdcccle control panel in linux.
2. After grouping all 6 monitors to act as one in windows, I can then enable Crossfire and both video cards provide the acceleration for all 6 monitors acting as a single monitor. This is used for gaming so you can play games FULL SCREEN across all 6 monitors - fully acclerated by both cards. In linux with the current setup - the amd control panel only lets you choose a single monitor to accelerate using crossfireX.
I'm fully aware of the xinerama layouts and how I can do some tricks to make all 6 monitors only show up as 1 - in fact I use something simlar to trick the panels in KDE to map to two monitors each (for a total of 3 panels) - however this is not TRUE eyefinity and doesn't allow me to group all 6 monitors to act as 1 to use full crossfireX acceleration..
In the windows control panel - eyefinity is enabled using "GROUPING" of monitors.. In linux I do not see this option and its only really just enabling all the monitors as individual displays - not TRUE eyefinity.
- Hope that helps clear up what I'm talking about - mostly it comes down to enabling true eyefinity with crossfirex so both cards can provide acceleration to all 6 monitors acting as a single display..