I've been doing a bit more work on various stuff, and have decided to drop the rated voltage. A 600 V rating means 600 V RMS – about 850 V peak for a sine wave. The issue is that certain components in the input (e.g. fuses, low-impedance connection relays) need to be able to handle the full voltage, and ones that can handle that voltage are quite expensive as a fraction of the total. So I'm dropping to a 300 V rating (about 425 V peak), which means I can use components with lower voltage ratings which are much cheaper.