ARC VT-100MKII to MKIII, upgrade worth the cost?

Thank you for your feedback. Leonard at ARC told me the sound is fuller with MK III. Do you find it to be true? MK II sounds very good but a little light weight to my taste. Also, they charge a fortune for retubing and financially it almost makes more sense to upgrade., unless I go for tubes from other retailers.
Any thoughts?

Mrwigglewm, that's exactly what happened to me, I tried to replace the driver tubes with JJ Tesla E88CC and blew the resistors and a transistor near the closest tube to the faceplate. These Teslas would not bias in VT-100MKII. I would probably not mess with driver tubes any more, however your describtion of Mullard sound is very tempting. Audio research is installing the 6922 for me. But I will try the KT-88. I talked to Kevin Deal at Upscale Audio and he actually recommended the new Electro-Harmonix KT-88. They are supposed to be even more dependable the Svetlanas.

Kevziek, the resistors smoked right at the moment when I started adjusting the bias. ARC just commented that the tubes are simply bad, I am not sure if it's true or not. I think Teslas draw too much voltage. The voltmeter went quite crazy. After my experience, I would not recommend JJ teslas for that amp and stick with the best vintages of 6922.

Gmorris, thank you. Kevin from Uscale Audio recommended me the 6H23. I decided to let ARC to install input tubes. Just too much hassle to bias them by myself. I might experiment with EH KT-88 output tubes instead. I will decide when I get the amp back and evaluate the sound with new tubes.