High gain is not necessarily the best thing for your tone. Also, different versions of similar tubes sound different. Some players like the high gain and 'hard' distortion of the 7025, which is MIL-spec, 'robust' version of the 12AX7A. If you like a good 'bluesey' tone, you might prefer a slightly lower gain 12AU7, or even a 5751 tube. These tubes all plug right in. The beauty of experimenting with preamp tubes is that you don't have to worry about biasing, and as long as the pin connections are compatible, you can swap them around until you find a setup you like.