Flycast Performance - Sammy

Hi Folks, I am using the flycast core for atomiswave and having some performance issues. I am running Metal Slug 6 (as an example) under windows 10 in Retroarch (i7, RTX2080) and seeing frame-rates drop from 60-30 or less. Now, I know its notorious for slowdowns but I’ve never seen anything like this and am left wondering if I have changed a setting and screwed things up?