Hi there,
natural history museum scientist doing a range of imaging from scanning electron microscopy, to light microscopy, macrophotography, dSLR, and even 4x5" view camera. Have used PS v3 - CS5.5 extended currently on Mac Pro. Imaging mainly for print publication, including >1000 page book designs with >1000 figures (QXP). Need rock-solid platform for large master files (100 MB - 1 GB) with excellent color management and proofing options. Efficient tool use is also critical: switching brushes, switching from adding to subtracting selections, changing units (much better in AP than PS), moving layers, scaling individual or multiple layers, forced orthogonal lines. Have to look into customized keyboard commands.
Looking forward to macro editor in AP, then I can mothball PS for good. Other functions such as heavy z-stacking (>100 x 300 MB 16 bit tif files) can be done with other apps (HeliconFocus, Zerene); PS CS5 stacking was worse than useless. Thus far very impressed with AP, and I just scratched the surface. Drawing speed on 4K NEC UHD 322 display is excellent. The absence of a license key is pure joy! Opens Canon 5DsR CR2 files no problem [no longer supported on any PS CS version].