What's your investment threshold?

This question only goes out to those like myself who enjoy the system gains running better cables bring.  Non-believers can save their money and comments for another thread.

Do you impose on yourself a percentage range for cable spending relative to other components?

Speaking for myself, I do consider cables to be a component decision worthy of budget, but I seem to have stayed in the 10-30% range of what I've spent on other components.  I can't see spending $1k for a cable on a $1k component for example.  I have spent $1,500 for speaker cables for a $6k amp.  That seems nearer the high end of my range but it still fits. 

I realized I haven't planned this as a hard rule, but that's kind of how this has worked out for me over time.  Anyone out there think a much higher percentage is justified?  I won't argue because these improvements are worth all the enjoyment you can get, so more power to you.