It kinda depends on how you use the internet. If you pirate software (which isnt the cool thing to do, kids), then AV is vital. Also, hacker sites and pr0n sites seem to pick up viruses as well.
If you use the internet for browsing, email, and other legal activities that involve popular and professional websites, etc, then, AV probably isnt that necessary.
I would still use one no matter what. Besides, with a computer like yours, you probably wont really notice a difference in performance anyways.
If system resources is your concern, most AV have the option to not have it constantly running as a process, but scans on demand, and updates on demand.