I did come up with a solution by using 2 512 byte buffers and I can play buffer one while loading data into buffer 2.
Sorry that idea is from the 1960s and I was there. Actually we used circular buffers which is a better idea. If you want to be more than a dabbler go to school.
You need to learn about the internals of SD cards and how that relates to file systems. That's how you get performance.