When building your loop there should be a list of things that come to mind, flow and pressure should be near the top of that list. Pressure drop is the measurement of inlet pressure minus outlet pressure, or the pressure lost of flow through the radiator.
The GTX was less restrictive than what I anticipated with the thin tubes and flow pattern. However, the thinner tubes and hot/cold side flow pattern do increase the restriction, so I included the pressure drop curve for the ThermoChill PA120.3 to show the increase. Just to give you some scale, popular EK and Enzotech chipset/mosfet blocks are more restrictive. While the GTX360 is more restrictive than a PA, that does not mean it is going to make a major difference in your loop, the Thermochill has an extremely low restriction curve. Charts below are PSI-GPM, kPa-LPH and mH2O-LPH to cover the imperial and metric audience.