AA
AIUI the STEC uses the Turn indicator, which is electrical, and is therefore entirely independent of the suction system. If you have a purely electrical a/p that has got to be the safest way to ensure that you remain the right way up until you are in VMC.
There is definitely a lag on the "DI" readout on the 530 (and I assume therefore the 430), which is not surprising when you consider the technology, but that lag is considerably less than that on the compass, and is quite useable if you make slow turns.
I would be very cautious before you assume that the altiutude readout on the 430 is independent of the static system. Certainly on my installation I have a blind encoder driving the altitude readout on the 530. You should check with your avionics engineer before you assume that the 430 is a backup to the static system.
Will