i have been using ImagesPlus for a long time now.. I like it but that's because it is the one I know.
It easily handles large sequences of images.. I routinely calibrate 100's of images (eg 5-20 hours worth of 3 minute subs). My laptop is not so powerful and it can do the same thing.. just takes longer but never stumbles.
I have a QuadCore desktop at home but I think for calibration it only uses one processor. The advantage comes when you want to do something else at the same time.. eg I will have one set of images calibrating while another is being aligned/stacked and I can still play with another image in IP or Photoshop.
IP is a great program but if I was starting from scratch now I would be looking seriously at CCDStack.. a couple of local astro colleagues wax lyrical about it every time I see them
Phil