Certainly the NISMO bushes will be worse for noise as they will be stiffer.
I have no back-to-back experience with PU bushes but they will not neccessarily be worse for noise.
PU has lower damping than rubber.
Damping is good in that it will absorb some energy.
However damping also will increase the "dynamic spring rate" of the bush.
Changing the spring rate changes which frequencies of noise that will be transfered by the bush.
Therefore it is possible that even if the "static spring rate" of the PU bush is higher that from a point in the frequency range the "dynamic spring rate" of the bush will be lower and less noise and/or vibration in that range will be transfered.
Some manufacturers already use PU in some bushes and it is very popular as spring aids/bump stops, it depends on the design of the vehicle and how much budget they had!
The only way to really know is to ride in a car with them fitted.
As for squeaking PU bushes should come with lubricant and the insides of the bush should have a patern that holds the lubricant inside the bush.
Also different bush manufacturers design replacement bushes differently. My friend has an E30 M3 and complained about the front suspension, putting down his issues to the Powerflex compresion rod bush. He replaced it with a Superflex bush who's design was visably and it was much improved.
I also have a friend with a highly modified Lotus Exige. He has tried Nylon, original rubber, stiffer rubber and now is on PU bushes. He hasn't complianed yet about them so they must be quite good!
Both these friends of mine are not boy racers. They do do trackdays but they mostly drive their cars everyday on the road (although I don't think the Exige owner uses it for the shopping!). Also they are both suspension engineers.
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