Cathode bypass cap rating for 2A3 Paramount

[triode]

Hi,

I want to upgrade the cathode bypass cap in my 2A3 Paramount with film caps.
The measured voltage at across those resistor are around 215v.
Would 250v rating cap enough or too close for comfort?
I understand that electrolytic cap should not stretch too close to the rating, but how about film cap like Solen or Mundorf MKP?
400v caps are a bit too large, since Mundorf parafeed cap already take a bit of space (not to mention more expensive too)

Thanks in advance

[Grainger49]

The time to check the voltage is when you turn it on.  It will be zero for a while but then it will climb and drop a little. 

Find a capacitor with a rating above the peak.  Higher will just make the capacitor larger and more expensive.

[Paul Joppa]

If you have the sort-start upgrade or the Version 1.1, then you would not normally exceed the 215 volts. If you have the older version, then you will always risk approaching 450 volts on startup. If the soft-start is misadjusted (as it might be when a tube is swapped), or if the driver fails, or if the driver socket fails, you are again at risk of approaching 450 volts. If the capacitor fails shorted, as electrolytics do sometimes, you risk consequent damage to the 2A3.

Those are the reasons that a 450v capacitor is specified.

[triode]

Thanks PJ,
 I guess I keep the electrolytic then.
Would installing a bypass film cap improve the sound? What optimum value for these bypass caps?
I'm thinking of using those Solen 3.3uF originally used for parafeed cap for the bypass. Would higher quality caps (like Mundorf) make significant difference or just waste of money?

Thanks