Hello,
it is difficult to say what is causing the differences, without knowing the schematics and all details. Typically the available memory bandwidth is different - so the data throughput to SDRAM and Flash could be different. In case the displays are different (either in resolution or in timing), the requested memory bandwidth could be different.
Please consider, that if a frame is missed, the system has to wait for the next one, e,g, if an animation takes more than 16ms, 60 FPS cannot be achieved and the result will be 30 FPS.
Best regards,
Manfred.