Thanks for the replies.
I should have been more clear. I am using the magnasight focuser, and I don't have much experience with it yet. The print that came out well was when my eye was about 6 or 8 inches away, and the one that did not come out well my eye was closer, maybe 3 inches. I've only been using the magnasight for a little while... before that I was holding a magnifying glass up to my eye and leaning over the print while focusing.
Also, now that I think calmly about it, my worry about the SLR viewfinder is overblown. My negatives are sharp and my notes about focusing match my experience printing ( i.e. occasionally I've taken a second shot when I thought the focus was slightly off, and the notes match the negatives perfectly. )
And yes the split prism and the "shmmery" area around it are excellent...
I got a little upset by seeing this difference and over-reacted.
I will also consider getting a nicer grain focuser! And some reading glasses too!