I have many 16x20 prints on 20x24. Sadly. Way too small for my taste, but at the time I could not afford bigger as I could get two 20x24's out of a full sheet (32x40). Image size is around 15x19, with a window cut about 16x20. I was printing full-frame 4x5 negs.
I found that 22x28 is great for vertical 16x20 prints, but lousy (IMO only of course) for horizontals. Way too much space on the sides compared to to top and bottom. Might work fine for full-frame proportions of 35mm negs.
I find that 24x28 looks great for both vertical and horizontal 16x20's. Again, image size is actually around 15x19, with a window cut just a tad bigger than 16x20. Love this as I get a usable 16x20 piece for 8x10 or 11x14 images!
The 24x28 requires more wall space than 20x24, of course, but I like the amount of white (~4") around the prints.
At least with LF landscape, a bad day of photography can still be a good day of exercise.
22x28 was AA's recommendation in The Print. After having some 16x20's on the wall for a while, I found that 22x28 didn't work for my 4:5's. Too crowded. I found bliss at 24x30 for all my ~20" longest dimension prints for 4:5, 3:5, and 1:2 aspect ratios.
I use 24x28 (actually 600x700mm) for my 16x20 prints. Window size is about 15x19.
You do end up blowing most of a 32x40 mat on each frame with some left over for framing 8x10s, but that's still way cheaper than the museum glass etc. Assuming you're not randomly changing the aspect ratios and can live with a standard 15x19 window, you can of course re-use the mat and change the print over occasionally.
That was my next question. Light Impression is pretty expensive. Do guy know of any other places that you ordered from that I could check? I'll check out Frame Distination.
I buy regularly from Frame Destination. I find the least expensive way to mat is to establish a few standard colors and buy boards in bulk, then buy a reasonably good mat cutter and do it myself. In less than a year, I saved more than what I paid for the mat cutter. (About $200)