I don't think that there is a need to change the James Cook just because of the dv it can have when it's fully loaded with fuel, 2400 tons of it.
According to the mission roster, there are 6 missions that dock with the Cook for supplies:
One XR5 (OFMM 5), two DGIVs (OFMM 11 and 18), one ShuttleC (OFMM 12) and two XR2s (OFMM 21 and 22). Even if the payloads of the ships in these missions consisted entirely of fuel for the James Cook, it cannot have more than 467 tons of fuel, giving it a total dv of 127 km/s.
If the only refueling mission is the XR5 and you calculate a factor of 0.85 for the dead weight of the containers then you get 367.2 tons of fuel, giving a dv of 107,6 km/s, which is close to what the Arrow has.
According to the mission roster, there are 6 missions that dock with the Cook for supplies:
One XR5 (OFMM 5), two DGIVs (OFMM 11 and 18), one ShuttleC (OFMM 12) and two XR2s (OFMM 21 and 22). Even if the payloads of the ships in these missions consisted entirely of fuel for the James Cook, it cannot have more than 467 tons of fuel, giving it a total dv of 127 km/s.
If the only refueling mission is the XR5 and you calculate a factor of 0.85 for the dead weight of the containers then you get 367.2 tons of fuel, giving a dv of 107,6 km/s, which is close to what the Arrow has.