[R-390] Another Capacitor Question

[Barry]

This question concerns voltage ratings. 

In this application, the system can apply up to 600VDC across the capacitors (several in parallel).  I happened on some 1000V polystyrenes for the bulk of the 0.5uF and need to finish with some smaller value polystyrenes.  I can get some 1000V capacitors for this, but they're pricey ($10 each in lots of two).  I can readily get 630V polystyrenes, though.

Is this too close to the max rating?  I usually get capacitors rated at well beyond the anticipated applied voltage (1.5x or better) and would do so here if it weren't for the lack of reasonably-priced units.

Thanks for any advice,

Barry - N4BUQ