Interesting that 10fp4 is still running strong. I tend to find that when a cathode/g1 assembly looks toasty like that, the tube has high miles and tests weak. I took some pics of a couple of 21" crts guns to illustrate this in this thread:
http://www.videokarma.org/showthread.php?t=246342
I just drug out a pair of 21" roundie crts, and the one with darker cathodes tested weaker than the one with less toasted elements.