Well, this what I did, an old boy on another forum I frequent suggested aircraft stripper from the auto parts store. It is really nasty stuff, eye protection, thick gloves, shop apron, etc are indicated. It is a gel consistency, I painted on a nice thick coat and let it work. The label says 5 - 15 minutes, but I found through trial and error that about 30 minutes was a lot better. Then blasted it with the pressure washer. Did better than I thought I would be able to. In a few areas it removed the paint stripes almost without a trace, most left a faint shadow but I can deal with it. A few other spots may benefit from a second application.
This was for striping a basketball court in the driveway for my girls. Last year I painted it in (using a stencil) for the first time. It was perfect, but in my ignorance I used Rustoleum Marking Paint (not as permanent) instead of Striping Paint. The old paint was so faded after 1 year that you could hardly see it, I just blew what remained away with the pressure washer. This year after re-spraying it I could see that the top of the key had gotten off a little, oh crap. I am usually of the measure-twice-cut-once school of thought, but I guess the stencil had moved and sort of bent without my noticing. I tried real hard to convince myself I could live with it till the paint faded, but it was just a little too far off. Now the driveway looks pretty good, ready for another go at it.
I'll get it right this time.