A 665R filter is basically a red glass filter, it would pass considerably more light compared to a RM90 filter. There is some academic debate on this but for photogrtaphic purposes the NIR spectrum starts around 720nm, these filters are almost completely opaque to visible light. Be warned, these dark IR filters are rather expensive.
Originally posted by erik_corrxx I noticed k3 may not be able to shoot IR since it cant see the remote light when doing that test
the K5II(s) and the K3 both have exceptionally strong UV-IR cut filters in them, I detected a stop and a half reduced sensitivity compared to the K7, and nearly three stops compared to the K10D.