Capturing details is important, but one is better off with multiple 1-2-3 mp cameras to cover properties than having just a couple 5MP ones.
While the idea of more megapixels may be better on paper, it really will depend on sensor size & lens quality for that to pan out. Like other's have said.
The highest mp cameras come in at a lot bigger price point and may not offer a great framerate for recording. Which is the worst part of multiple cameras with those extra megapixels. 5MP cameras drastically increase the bandwidth and storage needs. This may not be an issue for the each of the companies' budget, but, as I'm sure you understand, practically speaking, some system will have to process all the incoming data and save it. When you're talking commercial installs, you are pretty much looking at continues recording from lots of angles.
My vote would be for a balanced system with probably 2-3mp outside and 1mp inside.
Use cameras field of view to match broad coverage needs and focus on specific entry locations.
Which comes back to the 5MP thing, depending on the site, camera type, camera angle and its field of view, one can be recording a ton of sky, trees, shrubs, pavement, ... which would be a waste of pixels and storage.
Good luck with your project.
Hope to hear back about the actual installation.
