has anyone got the scrolling to move as fluid as in the videos?
Yes. (Note: I do not use a raspberry pi, this is just on my PC)
The trick to getting it to run smoothly is listed in OP's post, you have to resize all of your flyer images to 310px height. This is easily and quickly done with the program IrfanView, which if you don't already have you should go download it as it's free and the best lightweight image editor/viewer out there.
To resize your flyers easily, just do this:
Navigate to the top left corner of the screen and go to File > Batch Conversion / Rename
Check the box where it says "Use advanced options (for bulk resize...) and hit the "Advanced" button on the right.
Check the box where it says "Resize" and set only the height to 310px, leave the width blank.
Then navigate to the "flyer" folder of whichever game system's flyers you are resizing. (Should be within the "scraper" folder of your Attract Mode folder)
Select all of the files in the folder and hit "add", then hit the "Start Batch" button in the bottom left. Wait for it to complete and then navigate to C:\TEMP (Or whatever folder you selected for the resized versions to be stored in) and copy or cut all the files. Then just navigate to your Flyer folder, select all files, delete them and replace them with your new files.
This should get it running smoothly on most machines.. I dunno about Raspberry Pi's but I imagine it would help. I would recommend doing this anyways regardless of this theme because there's no sane reason to be using 1000px-2000px size boxart for any frontend.
The only problem I'm having with this theme is I have no idea how to get the background image to change to the right ones for each system. Mine is just stuck on the default.