I was getting about 3.8k post-NIE (with FCH) and had hit 5.5k 3.5 years later. Had been promoted to GEO4 (or the equivalent back then), though. So I guess this was considered faster than average.

Keeping in mind that I'd started about a decade ago, I think it's very possible for new officers with good performance to hit similar numbers today, even at GEO3 (taking into account salary adjustments and inflation).