Switched to a 2SC1624 with a 1k resistor to the Arduino PWM and I can get it up to 3000 now, but can't reach 4000 or 5000.
I've fried a couple 2N3904's already. If I lower the resistor value between the PWM and the base to 680ohms I can get the gauge to max, but I think it's frying the circuit in the process. With 1k things seem stable but I can't max the gauge.