I had the answer to this long time ago but for the benefit of others and who may be in the same issue.
Apart from removing shadows, you also need to remove "clear color" backgrounds. Any additional drawing that will require additional processing should be removed or replaced with an alternative. Any heavy lifting, text formatting, date formatting should be done before even showing the collection or table views. Make sure you cell only does the presenting and not processing. If you can't avoid it do the processing at another thread.
To measure the rate of the scroll you will need to use the instruments > graphics > core animation tool to measure the frame rate.
Try it and you will notice a difference.