I have had an email response which does not show on the forum - "I found out that McSvHost.exe was new with the 2010 upgrade. On my XP SP3 machine it was causing serious system degradation, using too much CPU. I found out that if I lower the priority to McSvHost to below normal my PC ran much better. However, I had to do this after every restart. Was McSvHost causing issues on your PC?"
My answer to this is no - I have not previously had any problems with the widely reported McSvHost issues.
I seem to have almost the exact same problem, except McSvHost also spams port 80 on all hosts on the local network with HTTP/1.0 requests. I am using McAfee Anti-Virus Plus and have known about this problem ever since I installed it around the same time as your post last year, so I assume this is "normal behavior", although it sucks for my server. My server logs are also saturated with logs of these empty HTTP requests, and it sometimes takes me hours to accurately calculate web statistics because of it. (I bet your McSvHost.exe does this too, but you don't have any HTTP servers on your network.)
As for the SYN packets, I believe they're used to determine what computers are active on your local network. (TCP/UDP Port 445, a.k.a. Microsoft-DS, is used for network filesharing on Windows systems).
Being that you never received a response to this question in nearly a year, it doesn't lend much hope to my question posted at https://community.mcafee.com/message/202429#202429. At any rate, I hope somebody answers this question in some official capacity at some point for both our sakes.