My guess would be that the preamp tubes will make a much more significant difference here. Unless you're driving your power tubes to the point of distortion, preamp tubes will make all the difference. I know Eurotubes sells high gain JJ sets. I like JJ's in my Renegade. Give them a try if you like.
I will say that depending on what brand of 80's modded Marshall tone you're after, you may not have the right amp. My Renegade does Hard Rock well but it is simply not a high gain, Metal amp. While the gain is generally there, the voicing is not. An eq pedal and/or a Metal style pedal is necessary to go in that direction - especially for modern metal. I've never gotten the impression that the Tweeker, the Rebel, or or the Renegade were intended for pure Metal use.
Someone here will surely correct me if I'm wrong.
Good luck.