very slow object selection

I have a problem when selecting object after a project gets to certain size or objects become too complex, I am not
sure exactly what the trigger is - it is very slow, up 10 seconds or so, which makes blender not responsive and very hard
to work with in that state.
I am only guessing that it is hardware or driver related, in which case I am not sure there is much to be done with my
current setup (win 7, nVidia driver - latest version, but it’s rather old) , but maybe it’s something else I am missing.
For some reason I fail to upload .blend file as an example, I will try again later.
If you know anything about the problem, I would love to hear…
Thank you very much

Do you have subdivide on any mesh?

alternatively you can just put different parts on different layers and then just render them together.

Yes, I do have a few subdivides, but they are rather gentle and local. But what is the essential difference between subdivided and non subdivided meshes, in this aspect ? is it merely a matter of faces count ? (I have objects with a high number of faces, but that is due
to applying array modifier)

You could simply bump down the number of subdivisions in View under the modifier.

A great way to help with a large amount of instances of high-poly models is to go under the Object tab and change maximum draw type to Bounds which will replace a mesh in the viewport with a rectangular prism and render the original high quality.

I rendered out a scene with 3,145,000,000 (billion) polygons using the below method, just changing draw type to Bounds.

Any application, when given a large amount of data to work with, will slow down. That’s pretty much a given. Even though the developers have optimized the crap out of Blender, there will come a point where the amount of data you’re working with–no matter how fast your CPU or GPU is–will slow down. It’s inevitable if you keep cramming things into a scene.

So, other than what DCBloodHound and MarkLaBarr said, you can also 1) click the “eye” icon on the subsurf modifier, or 2) if you have a lot of objects all with subsurf modifiers, go to the Scene Properties (third tab from the left) and look for Simplify. Turn it on and set the number of subdivisions low (or off, even). This does all objects on all layers in one go.