>My P550 didn't like SBC-27, even with the base-27 binaries installed. 
>Boot problems were similar on my Zip (although the exact point of hang-up
>evades my memory).  I left the base-27 in place but returned to SBC-25,
>which continues to work fine; in fact, I got ps to work, which was why I
>was trying -27 in the first place. 

The Performa-550 uses the Cuda chip for ADB.  The Hardware Direct code 
isn't completely funtional for all variants of the Cuda yet, and doesn't 
work reliably on the Performa-550. You'll need an MRG Kernel.  If you 
want you can get the one I built after a 4/19 SUP.  It has everything 
recently released in -current except it's an MRG based Kernel.

<http://users.aol.com/bobnestor/GENERIC.tgz>

If you need an SBC variant of this Kernel let me know and I'll put one 
together.

-bob