Normally, I don't just go and say upgrade - but at the same time, I will - SEP 11.0.6100.645 is nearly 4 years old - the 11.x platform in generall was brought out 2007 - which defined the overall engines as a whole, yes some things were patched to fix issues with compatiblity and defects;
Would you install Windows XP onto a new I7? I would hope that you would say no...why? Because features and how to OS works with your hardware is completely different then what was of the time back then...same goes for AV
If you are running a 7 year old AV product, how can you expect that it will run well with modern HW/OS?
In this case it is likely AV components are scanning literally every file in use, copying, etc...
TruScan / PTP can be installed on a 64-bit or Server OS machine, but it will not initalize...ever so that rules out that option
FW/IPS can possibly be an issue, however likely not the case (also as indicated by your own mention that you have disabled that option)
What are your scheduled scans set to? What is the prioritizaiton? - In this case, do yourself a huge favor - get 12.1.4 rolling on the network - features such as Download Insight will drastically reduce your overhead for resources used...but then also, look at the policies that you have in place too, I would suggest remaking policies and overhauling that as well, if you have problem policies, they may haunt you throughout your 'SEP Experience'
Just some ideas and suggestions and reaffirming what was stated above