Quote - Now using a 32 bit exr - I had to play with the displacement value a lot to get a similar result to the 16 bit map - and note the increase in render time ...

Re-render that again - a single pass is not representative, it's better to do a "best out of three" comparison.

Poser converts all textures to tiled mip mapped OpenEXR files before handing them over to FireFly, and it does that in a background thread. It may have been that your TIFF was already converted when you started the render, but the OpenEXR file had not been tiled and mip mapped yet when you started. The time it took to convert then became part of your overall render time. FireFly itself is completely oblivious to what file format the textures were saved in originally, since Poser 7 it only reads tiled OpenEXR through a texture cache. The tiling and the cache should in theory allow it to render billions of textures with ridiculous amounts of pixels each using just a couple of hundred MB of RAM - at least in our tests, we haven't found a limit in practice yet.