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Tee'ing the gauge in the pressure line anywhere from the pump to the cylinder should give the same results. What you are lookin at is the pressure the relief valve is set to, when it's bypassing at the end of the cylinder's stroke. As far as flow is concerned, note the cycle time of the cylinder. Then figure the area of the cylinder bore's diameter, multiply that by the stoke in inches, and you'll have the cubic inches of oil needed for a full stroke of the cylinder. There's 231 cubic inches in a gallon, so once you know the volume displaced by the cylinder, and the cycle time, you can calculate the gallons per minute the system is producing. Then you can calculate the area of another cylinder, and figure the cycle time for that alternate cylinder choice. The cylinder rod diameter (if it is a conventional type cylinder) will not affect the extension of the cylinder, but will affect the retraction time. The bigger the rod is, the more oil it displaces, and the faster the return cycle will be. As far as line size, unless the line size is so small in relation to the pump output that it can't take the full output of the pump without bypassing some oil through the pressure relief, the line size will have very little effect on cycle time. If the line is so small as to be restrictive, there'll be more heating of the oil, and if it's REALLY small, you'll get some bypassing, but otherwise it should be OK.
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