Why not just use a valve as a way to put a known restriction on the flow combined with a flowmeter? There is no real reason to replumb everything and test separately.
As mentioned, the results will depend on the radiator, the pump, and the waterblock chosen. The goal should be to optimize everything for a complete system and not to just choose impressive parts. Here is a graph from some of my playing around with my setup:
This is an Eheim 1250, a Maze2, and a 1975 Caprice core cooling a 1600+ XP. Temps were taken with a MAX6657 diode reader.
The GPM is varied with a ball valve and measured with an inline flowmeter from McMaster-carr. What you can see is that there is a fairly substantial change in delta T from 0.4 GPM to 1 GPM. However, above 1.1 GPM, there is no real benefit to increased flow rates with this setup. Now from experience, a 3/8" tubing and fittings loop with a heatercore and a Danner 250 was right around 0.75 GPM, and the same setup with 1/2" fittings and tubing was around 1.1. You can expect for this to be reflected in a performance increase. However, switching from a 1250 to the 1060 might actually worsen performance, as the block seems to already be performing at max efficiency and increasing the flow over 1.2 GPM will only serve to decrease the residence time in the radiator.
I said this earlier and I will say it again. I would prefer to use larger tubing and excessively large/drilled out fittings and a smaller pump to get to 1.1 GPM rather than fighting the resistnace and friction of small tubing and fitting by adding a larger pump. I actually hope to move down to an Eheim 1048 in my project case...