~30K the Behringer Truth 2030A are pretty decent, @50K the Dynaudio BM5A are the way to go, @1L you can probably squeeze in the Adam A6 or a pair of Genelec 8040. Genelec also has some ~40K models, they may be worth a look though though they need subwoofer assistance.
NS10M were *not* flat - they had a super-bright top end, too hot by about 3dB. that brought out a lot of top-end detail so one could correct sibilants, but the NS10M were far from being good monitors to mix on. They were popular, no doubt, but in a small section of budget studios - the big guys were using Genelecs
In truth monitors are less about overall frequency response, and more about how comfortable you are listening to them for long periods of time at reasonable volumes (75dB+). If you monitor at low levels your mixes will turn out bass-heavy and bright, so it's important to keep levels high enough to mix right. But that's just me, your mixes could turn out very different.