7062First, look at this thread: http://www.artsandmedia.com/5965.html
The differences to these tubes when they are being used with VT-231s are small. They all sound good, and the major difference is gain. The best tube for me is the Amperex pinched waist, but all the 5965s sound pretty good, and the 6414 is, of course, lovely.
When you do use these tubes as the input for VT-231s, you will find enormous differences between the VT-231s. I have Slyvania Bad Boys, Regular Sylvania VT-231s, KenRads, Raytheon, RCA and NU. Each one has a very distinctive signature that you can hear immediately.
Don't spend a lot of money (more than $25/tube) on 7062, 5965, 6414, 12AV7, or 6829. These tubes may sound different on other amps or with other outputs, but on the SP MPX3 Slam SE, they just don't make much difference, other than for gain.