[plt-scheme] two questions about extensions and 3m under 372

1. What experiences have people had moving their existing MzScheme 
extensions from CGC to 3m?

2. What experiences have people had opting to stay with CGC?

Background details follow...

I'm helping to move a system deployed under PLT v300 to v372.  The 
system uses multiple in-house MzScheme extensions written in C.  We 
therefore need to decide whether to use the old CGC or 3m.

My main concern is the unknown risk that I will make an error in the 
conversion of the C code to 3m that won't manifest until this system is 
deployed to customers under 372, which would be very bad.  (Perhaps it's 
easier to write for 3m from the start, rather than have a different 
programmer convert after the fact.)

I don't know the likelihood of error if I work very diligently, nor the 
likelihood that any such error would be detected before deployment.

By the way, any eventual move to PLT v4 is not a concern for this system 
at this time.

Thanks,
Neil