PJZ - you're right - thinking about it, I should have known this. 

While making my James texture last week I loaded the .psd files in the material room to save re-optimising and saving as a jpg every time I wanted to render the latest version. There was no appreciable difference in render time to using the optimised jpg. 

So the only difference to the end user, once the texture is actually in Poser, will be the time spent downloading, and the space taken up on the hard drive.

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"you are terrifying
and strange and beautiful
something not everyone knows how to love." - Warsan Shire