No opinions or hearsay just some guidelines:

• Gamma — 1.8 to 2.2 (or L*).
• White point — 5000K to 6500K.
• Brightness levels — 80cd/m2 to 140 cd/m2

“One additional, but little known fact is that many printers routinely re-separate CMYK files to better match their press conditions, or even to save ink by trimming total ink coverage and/or increasing GCR (grey component replacement). Some printers use Photoshop to do this, which while not optimal, works, while others use device link profiles, a better method.”

Source:
http://www.updig.org