After a lot of experimenting and wasting a lot of paper and ink, I finally got it working the way I want. My borders are perfect! (using Retain Size). Not only did I have to make the image 10.25", but also had to create a new paper size of 10.25. I had to make my image slightly off-centre - a little to the right, AND place the image as a 10.3" image in LR on the page in LR. LR wouldn't go 10.25 and rounded it up to 10.3.
I then just duplicated the paper size for the different lengths to print mulitple 8x10s, one after the other with no gap - and then trim myself. For example, 2 10x8" (horizontal/landscape) images have a paper length of 16" (by 10.25" wide) but you also have to add about 1/2" to the length because the printer doesn't start printing for about 1/2" into the paper. So in the layout in LR, you also have to be sure to place your first 8x10 about 1/2" down the page.
The problem was the same printing through PS CS5, but LR was easier to set up different presets for the page sizes and print options.
Oh... and I just turn the paper cut to Normal and I get about 1/2" of waste before and after the print job.