I run Windows XP SP3 and use Avast free 8.0.1489 with Agnitum Outpost Firewall Pro 8.1 and EMET 4.0.
I am delighted with Avast 8, have had no problems with it and system performance is excellent for an ancient AMD Athlon XP 3000+ based system. It appears effective as a defence. I do not use the Updater as I have other trusted arrangements. I like to make manual choices in the area of managing software updates.
I was glad to find that the Windows 8 Metro inspired GUI is easy to navigate and to read.
Hope you keep Avast available for XP users after April 2014. EMET 4.0 is especially valuable as a last line of defence but one which I do not wish to solely rely on.
Avast Email Shield is very capable and the SSL feature is great and allows me to use Virgin email.
I cannot recommend Avast 8 highly enough.