@Tony Cole
Since your PC is killer machine, I think there is no need to switch, especially since you already bought license for kaspersky and never feel any problems along with it. But if your license about to expired I think it's also a good idea to try Avast, avast is very good AV, low FP's, light and can be running smoothly even on low machine, and it's free (for the AV version) in my opinion..there is no need to buy the so called "Internet Security" or "Total Security" and "Extreme Security" since we can achieve that by using freewares, and does the better job. However if you doesn't feel right by using "free program" then it would be a good idea to stick with kaspersky or buy the full version of avast just to support the product
(only if you like it of course)
[EDIT]
About which one is good, both are very good product and both can provide almost the same protection, although Kaspersky won better protection, but in terms of lightness avast won, which one I vote? well it's depends...if I have a PC like you and the money to buy..I would go for kaspersky, kaspersky is quite expensive on my country, probably the most expensive than the others, the price it's insane even just for an "Antivirus" but if my PC it's not good enough, my vote goes for avast, besides avast also give a free version of their product, it's the least I can do to support them