Actually, 600Ω.
I'm not sure that it matters a hill of beans, anyway. Here are three identical bridges excited with 2mA, 10ma shunted by 600Ω, and 4.8V. The RTD resistance is varied from 75 to 125Ω.
The top plot pane shows the differential output of circuit C (the other two are the same on this scale).
The middle plot pane shows the difference between the output of C and B, and the difference between C and V. Note that the largest difference is a measly 66uV (out of 25mV) of this range.
Finally, the last pane shows the actual current through the RTD in the three versions of the circuit.
Driving a four-arm bridge with a constant-current source vs a voltage source has benefit when the tempco of the four arms is matched. By definition, in this circuit, the four arms do not have the same tempco, so why bother driving it with a constant current source, anyway?