I'm thinking about retubeing my amps with some Svetlanas. On Musician's Friend's website, they offer 3 options: Hard/Blue, Medium/Green, and Soft/Red. Now, I know that in the Groove Tubes grading system, 4 thru 6 is supposed to be ok for Boogies. Am I to assume that Svetlana has a simular grading system & that the Medium/Green is in the safe range for Boogies? I've heard alot of good things about Svetlana's and I think I could money and get a better tone by getting these instead of the overpriced Mesa & GT tubes.