Yeah, 565 is always going to be faster, make sure you setup your EAGL context to be the same format, for a little perf and mem boostie.
If you can get away with it, do all texture coord's calculations on the Vertex shader, it is what apple recommend, supposedly it doesn't get the dependent texture reads. I haven't tested it at work, back in PC land atm. Might have a looksie later, now that my daughter is in bed. (11 months old in 2 days
).