preamp tubes, gain, distortion?

[samuel1]

Would putting a higher-gain 12AX7 or 12AT7 into this preamp:
http://olcircuits.com/olc_eclipsevalve.html
cause the tube to distort?

When someone says the 12AX7 cannot handle much current, what does that mean? What is the practical result of that pitfall I mean?

How does the "mu" measurement fo tube gain (12au7 20, 12at7 60 etc etc) compare to gain measured in DB?