Yep, V4 can really push your tone around. I have tried 5 types of 12AX7 in V4 and in conbination with the other tubes, the long plate JJ works best. A chinese Ruby was good too. As for the 12AY7 I guess there are not as many to choose from. I am currious to try a 5751. SRV was said to use those (probably V1 for his amps) to tame things down.