The 250 Hz cut does improve the clarity in the mid and upper voices, but it so thins the bass that it's probably not going to sit well with your bass player. It's turning a meaty performance into a "whimpy" one. Sorry, I know that's not much help and is something you already know.
Have you run run this past the performers? In the end their opinions matter much more than ours. They are likely most concerned that each instrumental line is heard and are probably less concerned about the room sound and will understand the limitations of performing and recording in a less than great space.
Last week I recorded a string quartet in a small church which had a beautiful, smooth, uniform reverb. Unfortunately, it also had an air handler that had a broad spectrum of rumble from 10 Hz to about 200 Hz that could not be turned off during the performance. I used a 24 dB./octave filter at 50 Hz and a shelf of -4 dB at 110 Hz, but that was the most I could get away with without adversely affecting the cello sound. The program included some works with very soft passages, so in places the rumble was audible. I was not happy with the final mix (I used a pair of ORTF MKH-8040s, a closer pair of DC-196s and a spaced AB pair of MKH-8020s). Anything that included enough room ambience had too much rumble. Anyway, the musicians didn't care at all. They just wanted to be able to hear the string voices properly blended and balanced.