RE: aluminum parts vs plastic parts
Rpm have a good rep, but they aren't infallible. Their Slash rear hubs are weaker than stock, and their rc18 bumpers are known for shattering easily.
STRC make seriously high quality Slash parts, would not hesitate to put those on in place of plastic. In fact I didn't. I've got a good portion of the catalogue on mine, never so much as popped one of their shock caps.