Alpha (Non)Premultiplied RGB for PNG files in GapiDraw?

Does anybody have experience, if it is better to use Alpha Premultiplied RGB images in PNG files, or Alpha NonPremultiplied RGB values in PNG files? I mean for GapiDraw functions of course.
The difference can affect both intensity of transparency and a speed, because AlphaPremultiplied RGB values requrie only one multiplication to compute with background.
With regards,
Rene.
The difference can affect both intensity of transparency and a speed, because AlphaPremultiplied RGB values requrie only one multiplication to compute with background.
With regards,
Rene.