[R33]

I cud only speak through experience as I don't know much abut engines etc. The 4g63 sounds loud and booming, especially when they are married to apexi titanium exhausts/hayabusa. The SR cud also sounds almost similar.
They are not that high pitch-ed but yes, they lack the lower note/grunts of the RB. On the track, I could easily identify the Evos/SRs coming down the back straight before they appear on the front straights. But The Rb26 always sound "fuller" and the note is always "lower" than the Evos/SRs on full steam.
But the idling notes...the RB26 is much softer than the Evos/SRs. The notes from the STi are pretty sick at low rpms. I like those!