Bitdefender works very well but it's one of the slowest virus scanners I've ever seen. That Murphy sheild thing can be a bit too intrusive too; you either have to disable half the features or switch it off when installing programs etc because it likes to ask confirmation for just about anything an installer would want to do (writing to registry, system directory and everything!).
Maybe it's worth a try? It does it's job well, and if you're happy disabling a load of stuff to make it run better then it could be what you're looking for.
BTW, I found F-Secure to be very sleek and it didn't impact performance too badly. But I think the best virus protection is common sense combined with manual scanning of all downloads, a weekly system scan and the use of good email clients (not Outlook). Why check all your files all the time, slowing down the computer? Seems pointless to me! The only time I ever had a virus was when I entrusted my system to Norton AV 2000.