As most print shops still use 8 bit printing I wouldn't worry about bit depth, although it is nice to use a higher bit depth when processing the raw. If you ask your printer whether it would improve the image by increasing print files to 16 bit he will give you the lowdown on what you shou be using. I only use PSD files for saving files with layers intact, otherwise I use tiff for printing. I stopped using aRGB too because if the print shop doesn't handle the larger colour gamut with their print process what's the point of sweating your guts out to perfect the colour range?
Here is a very short video opinion on the subject. Excuse the intrusive add on the front of the video.
http://www.5min.com/Video/16-bit-and...ints-148102440