I use on my Single Recto a pair of JJ 6v6 tubes that I ordered from Eurotubes on the EL34 mode.
I love how they sound! They are awesome, I really like the low end that they have.
The cleans are very cool because those tubes puts the fixed bias right where they should be, even the hottest 6L6 cant do that.
Try them and you wont be dissapointed!
Im running my amp with those tubes for about 6 months without any problem. Dont be afraid to use them (the JJ6v6 from eurotubes for Single Recto, havent tryied any other, they have to be that grade so they wont fry your amp)
About the Loudness, well, they suppose to make your amp run about 25 o 30 watts, thats just 5db or so less in volume, so it will still very loud but will breakup early.