Search the archives aas boyth have been discussed many times. Either would do a good job. They are both different sounding preamps. Keep in mind that the RED-8 does not have the fine gain control setting detail that the Grace has.

While I recognize that the Grace might not be everyone's cup of tea, I personally love them. Clean, accurate, and detailed. I used to work in a studio that had the 8 channel unit. I miss them dearly. 2 bluegrass records I made in that studio using nothing butt grace pres except on vocals where compared to Allison Krauss records sonically. How often do music critics even stop to notice that stuff usually? They are cream of the crop on acoustic instruments and drum overheads/rooms. If you pull your 421 back about 6-8 inches they sound great on toms. Pretty good on elec gtrs. Not all that on kick/snare/vocals though, way too clean for my preferences. A great investment overall and they have impeccable cusrtomer service. Can't say enough about that these days.