Originally Posted by kalnaren
Correction: The upper on the real P90 is metal, not polycarb.
My apologies. I had thought it was metal, but had been told otherwise from a somewhat reliable source. I have been unable to confirm this as of yet. I suppose the main point being that once properly painted, the fact that the upper receiver is made of plastic does in no way affect the solid feel and overall perception of this particular model.
To add to what KND said about the piston, yes, to some it may be better to have a plastic-toothed piston for the reasons he stated. However, I have experience with both where there have been positive results using steel toothed pistons. I have one in my MP5 and it has performed beautifully for a number of years running on Lipos.
That said, it is still a risk. A $20 piston is cheaper than a full gear set, especially with a mechbox that is so easy to work on.
Checked the ROF: 19 RPS with an 11.1v Lipo and M100 spring (which is slightly weaker than the stock spring), after it was gamed last week at TTAC3. I'm going to charge it up and see what the difference is. But 19 RPS is still quite decent.