@dankcushions arrrrgh. Thanks. Definite performance issues when rotating the whole system, and PiFBA is the only core that's giving me issues otherwise. Now I'm off to see if I can compile FBNeo with Cyclone and see how that runs. Thanks for your help!
Please do not post a support request without first reading and following the advice in https://retropie.org.uk/forum/topic/3/read-this-first