Another developer is recommended (e.g. A49). But even then, you’ll struggle to go above 1000 ISO. In low light, the shadows close in very quickly.
If A49 isn’t to your liking, XTol produces an identical curve with Neopan 1600 and achieves the same speed (1+1 in each case). The shadows always wash out; when measured at Zone I, the film has no more speed than a Neopan 400. However, due to its distinctive curve (steep shadows, normal mid-tones, soft highlights), it performs very well when used at higher settings in typical available light conditions.
Best regards
Stefan