Using big art like flyers can affect the performance of the pi drastically.
Back in the days when I was optimizing newer xmbc themes to work on my trusty 1st gen xbox - the trick was to lower the resolution of all images. The size (not the pixel count but physical size) was not the problem - only the pixel count. Maybe you can try that - resizing all images to have appropriate pixel count for low-res display.
For example:
with 640x480px layout resolution - marquee res could be 220px in width instead of let's say 400px
Maybe that's not the case with RPi, because xbox main problem was the lack of ram - and scaling down images really helped to save some resources. But you could make quick and dirty check by resizing ALL images by 50% with some batch resizing program - and checikng if it helps with performance.
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The other tip I can share is to stop using surfaces. When I was testing the themes performance on older mac - the difference was huge, like (of the top of my head) 20% cpu without surfaces and 60% cpu with surfaces. And I was testing this with ROBOSPIN - with only surface being the cab screen. Of course it was on mac and with older (1.6) version of AM - but maybe ditching the surfaces can help with RPi performance issues.
I took some quick and dirty 10 sec videos of various layouts running on one my crt.I've checked out that link... and it's probably bad link, because it leads to the uni_cade.zip download