Not suggesting that Mcafee is the entire root of the problem, but it's the last of the truly resource-sapping antivirus suites now that Norton have woken up and improved their own product.
Ditch Mcafee for..well...almost anything else really. The only paid-for AV I would consider is Kaspersky or NOD32, Avast or Antivir for freebies.
Need some details of your new system, processor, memory etc. Without that nobody can tell you what to expect from it.