Yeah the larger ST50's are darker so use a smaller gamma setting and possibly higher brightness setting.
On my 50ST50 the gamma at 2.6 looks good now, but early on it seemed to dark, so it gets better as it ages more.
I calibrated the basic settings with a calibration blu-ray disc since there may be slight variation from set to set. My brightness calibrated is 60, up a few points from d-nice. Can also bump contrast up a few points if you need a slightly brighter picture.
I also preferred Warm1 vs Warm2 color temp, to get whites a bit better for me.