The SDK methods RecordedValues, RecordedValuesByCount, InterpolatedValues2, InterpolatedValues, TimedValues, Summaries2, Summaries are close to about a magnitude slower in 64 bits as they are in 32 bits. I wrote some visual basic scripts that pull summary data using the Summaries2 method that highlight the disparity.
Using the randomly generated tags BA:CONC.1, BA:LEVEL.1, and BA:TEMP.1 for 1 day of summary data at 1 minute intervals returns the following timing.
BA:CONC.1 32 bits = .04 seconds, 64 bits = .31 seconds
BA:LEVEL.1 32 bits = .05 seconds, 64 bits = .31 seconds
BA:TEMP.1 32 bits = .05 seconds, 64 bits = .31 seconds
As a product developer that uses the PI-SDK, it becomes hard to recommend to a customer that they should go to the 64 bit SDK with these kinds of timings. It would be faster to use a 32 bit COM executable server that pulls data from the 32 bit SDK and marshals the resulting data across the 64 bit process boundary.