My environment is similar to yours. I'm currently investigating performance complaints which are believed to be associated with VSE DAT updates, but am yet to obtain firm proof.
Please forgive me if I'm telling you things you already know... I was not aware until recently that the VSE local update task is controlled by policy and is different from the update performed by an ePO assigned task through the agent. In the VirusScan Enterprise 8.7.0 User Interface Policy, the default policy has "Display managed tasks in the client console" and "Disable default AutoUpdate task schedule" unchecked. If the latter is not checked, your VSE update task will run independently and in duplicate of any server applied task. The former option allows you to see server applied tasks in the VirusScan console. In testing, I also determined that update attempts were occurring at every policy enforcement for me because my VSE deploy task was scheduled to run at every policy enforcement. (http://community.mcafee.com/message/110886)
One of the performance issues I encounter on laptops was believed to be McAfee related but I was later able to rule VSE out as the cause. At this point, the root cause appeared to have been Window's "Client Side Caching".
When troubleshooting reported McAfee performance issues (that I am able to witness) I like to use ProcMon to see what's truly being accessed while the CPU is pegged. Be aware that running ProcMon will also take a fair chunk out of the processor. (http://technet.microsoft.com/en-us/sysinternals/bb896645.aspx) This is nice because you can see if files are being accessed, and if processes are running, that have nothing to do with McAfee.
5) DAT Update time is Repeated Daily between 7AM and 10PM every 3 hours with a 2 hour randomization and a Run missed task with 15 minute delay.
I have not heard too many people complain about the utilization on these computers. We also run the Engine, SuperDAT, and HIPS content on the same task.