Registar will beat anything!
That being said it does not work in 32/64 bit linear mode like PI.
What I have done for 'difficult' mosaics is to save the 16 bit registered images from Registar. Crop them as a new image and then use PI to 'align' these already aligned images with StarAlignment in PI and then use Gradient Merge Mosaic.
The inherent problem is that any image is a flat projection of a spherical image. Registar is far better at distorting to match images.
See post 11 here
It explains how to set parameters to make PI 'distort' more.
http://www.iceinspace.com.au/forum/s...d.php?t=155620
Registar is now 64 bit and there is almost no limit to image size or number of images. It is well worth the money.
Another way is to align your images with an image generated by Starrynightpro or similar with Registar and then the resultant mosaic image will have the least distortion due to the mapping of spherical to planar fields.
Bert