While I am familiar with xrefs I've never seriously used them.  The nature of my work is such that there isn't a big need for them although I suppose I could force myself to utilize them if I cared to.

That configuration looks pretty good to me.

Now if your 3D drawings are over 50GB in size you may see some lagging but you could always resort to utilizing xrefs and/or freezing layers to cut down on the performance hit.

Not too shabby.  16GB of RAM should be sufficient for some fairly big 3D drawing files.  I have 8GB on my home system and 12GB on my work system and I have worked with file sizes between 24 and 38GB although those are on the high end of what I normally work with.

Oh, it's a laptop?  What does it have for a video card?  How much RAM is onboard?

The Overkill command can be found in Express Tools.  It deletes duplicate and overlapping lines. 

That's not much to go on so it would be tough to offer any advice.

You should use the command line version of purge as I called it out (with the dash in front of the command).  Purge Regapps first; rerun the command (with the dash) and this time select the All option.  Then run Audit and tell AutoCAD to fix any errors it finds.

Do you ever run the Overkill command on your drawings?

Simple and small AutoCAD drawings should not be crashing a balls-to-the-walls system.  If they are then there is something either seriously wrong with the files (corrupt) or your system as a whole.