It might be better to mix a free Antivirus with real-time protection (such as Avast) and free Malwarebytes for optimal performance. You have the anti-virus (which has a bigger database of malware than an anti-malware) as a catch-all. Then, you can use the anti-malware whenever you feel you need to scan your PC. Not only is it free, but it also will allow for better performance than using two protection programs with real-time scan. That will definitely slow down whatever you're doing.
P.S. I'm not arguing or anything, just suggesting a free alternative...