IF you're planning on buying a GDLP anytime in the future, than you can scrap the idea of any Shapton ceramic stone coarser than the 500 grit. The GDLP instructions specifically caution on using the GDLP for lapping any stone coarser than 500 grit.

I own the GDLP and among higher grits, I also own the 500 and 1000 grit Shapton ceramic on glass stones. I have not had a significant amount of free time to hit the restoration and honing activities hard lately, but when I have, I have rarely used the 500 grit (I'm OK with that since I'll use it for wood chisels and plane irons). I find that the 1000 works well and works quickly for me. Actually, for factory edges of excellent condition vintage razors (I have a few), I purchased the Shapton 2000 grit ceramic on glass and just don't want to set bevels on even the 1000 for those kind of razors.

Rather than buy the 500, I would recommend you start at the 1000 and set bevels with that. If you find that it's not as fast as you'd like for the type of razors you're needed to set bevels on, you can always buy the 500 at a later date. Just my 2 cents. For me, the Shapton 1000 is such a pleasure to use as it's smoother and gentler to the edge than a D8E which I've also owned and used.

Chris L