Do you like hard stones? And how important is feedback to you?
I have both a Shapton GS 1k & 4k. AFAIK, there's only the 4k & 6k so those are your options for that grit range.
I actually like the 1k a lot. It's incredibly fast cutting - the fastest in the range that I've tried. Unless you are trying to do serious repairs/metal removal, there wouldn't be a need for you to drop to a lower grit. It's a true splash & go and it's small and compact, so it's nice to bring to work with you.
But I dislike the 4k just as much. The feedback is horrible on it and if you aren't confident with your technique, it's very easy to round your edge and it'll do more harm than good. Even with good technique, I don't think the edge it leaves is all that great and I much prefer the one I get off my Rika 5k. But I also like soakers.
If I was going to do it again, I'd probably buy a Shapton Pro 1k & 5k. They're larger, softer, and with a bit better feedback. Their case also serves as a stone base which is convenient for work - the Glass Stones are so thin that they really need a holder or some sort of elevated pan set-up, which isn't practical mid-shift.