Digital BW, The Print

Hello...I am a hobby photographer but get the occasional  
job......most often musicians promo shots, and pictures of bands and  
vocalists....these usually are requested to be in Black and white, so  
that is how I got into digital B/W. I have learned a LOT from this  
group especially from paul roark and clayton jones. Right now I am  
totally satisfied with my 2400 and epson papers like VFA, premium  
semi-matte, semi-gloss, premium luster and for 4x6 prints, premium  
glossy.

Now I wonder if there is a best image size for a given paper size. I  
have many prints in 16x20 frames.  Some of the images are 12x16, and  
some are 11x14.....is there a standard image size for a 16x20 frame?

Also, for promo shots, should it always be 8x10 (4:5 ratio) or can  
they be at the 2:3 ratio in portrait mode? would they then be 6x9 on  
a letter size sheet? I just made several prints for someone and  
instead of cropping I just left them full frame and printed 6x9 in  
portrait orientation. (I took the shots today, and he needed them the  
same day for printing in a program for a concert series) I am  
surprised that I like them as well as 8x10, or maybe even better than  
8x10. I wonder if the graphics people are going to be bothered by the  
2:3 ratio.

Are there solid rules of practice regarding this stuff? Is there a  
resource, like a website or group that I could check out? Thanks  
again for all the help over the last couple of years. Have a good  
one...... Doug M