630 V version has thicker film. Tom Thiel (and his sources) is confident that will sound better. We are putting 630 V on the coax feed (ie, 14 and 28 uF caps) for maximum SQ. Where you are runnng in parallel to get proper capacitance, you might use a 250 V for the heavy lifting and 630 V for the final icing on the cake. Eg, 25 uF 250V plus 3 uF 630 V for 28 uF cap. The 43 uF subfeed cap is downstream from a 16 ohm resistor and will be a 250 V CSA. Elsewhere, I will be using 250 or 160 V caps, except for the Multicap bypasses which are 600 V.
That said, have fun and please relax about getting this “right”. CSA 250s are certainly going to be a notable upgrade over the OEM caps!
MRA-12 will give you more headroom compared to the OEM 10 W resistors. That is good!