Best temperature for optimum tube performance

Is there an optimum temperature range in which tubes perform best?
I've been running tube amps/preamps for over 40 years and have always placed a small, quiet fan in front of them to prevent excessive heat build-up (a modified, two-door antique silver cabinet is where they reside).
I'm aware that electrical resistance increases in proportion to increasing temperature, but am I somehow decreasing the optimum performance of my tube components with this strategy?