Do you know what the specs of your current tube are?
5k, provided it's in a decent housing is pretty nice. Also, provided that the tube specs aren't shit. If they're shit, don't bother. In the grand scheme of things, spending another 1-1.5k is worth it to most end users to get tubes that they're comfortable with.
As a general rule of thumb:
30+ SNR
<1.0 EBI
<1.0 Halo
2000+ FOM.
I personally prefer quality screen cosmetics over higher specs but that's just me. I can't stand looking at blemishes.