AN096 gives performance figures for CC1101-CC1190. 250 kbps, +/-127 kHz deviation and 540 kHz RX filter BW gives typically -101 dBm sensitivity. Increasing the deviation to +/-165 kHz and RX filter BW to 650 kHz will give similar performance (-100 dBm would be my guess). For the same deviation the increase in RX filter BW will give a theoretical degradation of 0.8 dB, but increasing the deviation will give a slight increase....
In order to increase the output power you can use 4-FSK modulation as this will lower the PSD for a given power level. You will most likely take a hit on the sensitivity so maybe not an improvement in link budget.....
Anyway, if you want to check out 4-FSK: For the same throughput you can the use a symbol rate of 125 ksps. According to CC1101 data sheet 250 kbps, 4-FSK, +/-127 kHz deviation and 406 kHz RX filter BW gives typically -96 dBm sensitivity. The 6 dB BW will be too low using these system parameters. 250 kbps, 4-FSK, +/-200 kHz deviation will probably be OK in terms of 6 dB BW. The output power can be increased compared to 2-FSK. Sensitivity: The RX filter BW should be 650 kHz. Not sure about what the sensitivity will be, but the increase in RX filter BW from 406 kHz to 650 kHz will give a theoretical degradation of 2 dB. The increase in deviation from 127 kHz to 200 kHz will counteract this degradation, but hard to say by how much but not by more than 1 dB.