You could submerge it and measure its displacement to find its total volume, and fill it to measure its internal empty volume. Subtract that from the former and you get its volume in relation to mass. Weigh it, and divide its mass by its volume to find its density. The density of copper is about 8.94 g/cm³.
If you have an ohmmeter, you can measure its resistance. Calculating resistivity will then be a bit more challenging, as it involves multiplying the measured resistance by the cross-sectional area (which you'll have to make an educated guess on from external measurements and its empty volume) and then dividing by the length between contacts. Copper's resistivity is 1.7 x 10^-8 ohm-meters, more than five times less than nickel.
Optionally, if you really do have full freedom, you could straight-up take a cross-section of it. That'll let you visually inspect it, and will make measuring its density and resistivity much easier and more accurate.
What do you say? Are you up for some investigative journalism?
Anyways, like you said, with the PLX chip the board runs much warmer, even with only one graphics card. I would be fine with the PLX not being there in the first place, but since they attached the VRM heatsinks to the PLX to help dissipate the heat, the VRM heatsinks have to handle much more than just the heat generated by the VRMs. Being able to carry out that heat with water would be very advantageous for me.Edited by gftgy - 10/6/15 at 1:36am