Is the 'salt and pepper' missing from the clean or the gain channel? If it is missing from the gain channel, swap 6L6 tubes for EL-34s. You'll hear that midrange bark start to come out more in the distortion tone but the clean suffers a bit. If it is the cleans that are lacking, I STRONGLY suggest running a duet of yellow jackets and el-84s with a duet of 6L6s. This will drop the amp down to 60 watts but as a trade off, you'll get this beautiful bouncy chime added to the cleans as well. You'll get more detail and thickness in the mids of the distortion tone and this may or may not be what you want. I would not recommend mixing yellowjackets with EL-34s since the plate voltage for these suckers is much higher and I hear it can cook the resistors in the Yellow Jacket
converters.
Speakers are SUPER important. A mix of v30s with g12T - 75s will add some chunk and thickness to the tone. I find the marshall cabs have more midrange and they're less thumpy and dark than mesas are. There is an openness to the tone which is really attractive. I personally LOVE speaker blending. v30s are very dark and tight speakers with a pronounced high end spike. They have lots of bite but mitigating that with a speaker that has a slightly different voice retains the pleasing characteristics of the v30s but rounds out the unpleasant ones.
V30 + C90 is popular. This is a tight and dark combination that doesn't really change the overall tone of the v30s much. Supposedly yields better cleans and lead tones but DEFINITELY is more balanced without the 'ice pick' highs. My next 2 x 12 will have this combo. 240 watt 4 x 12. 120watt 2 x 12
v30 + G12T - 75 is popular. I haven't tried this one but from what I have heard, it is phatter and crisper.
240watt 4 x 12. 120 watt 2 x 12.
V30s and G12ms is also popular. This is one of my favourite but it is more for punk and rock than Metal. The tightness and bite of the v30s combined with the loose cream of the G12m gives the perfect rock or punk tone. Very WARM. This is what my current 2 x 12 has.
50watt 2 x 12. (cant use 100watts through this) 100watt 4 x 12.
G12H 30s + V30s is also a favourite of people as well. You end up with more bass and less highs with this combination, as well as vintage warmth.
60watt 2 x 12. 120watt 4 x 12.
For cab models, look into Marshall, Mesa, Orange, and Mills Acoustics. Avatar speakers also has some reasonably priced 4 x 12 and you can load them with whatever combination of speakers strikes your fancy.
In MY opinion, the oversized STANDARD rectocab has a lot of highs and lows and is more scooped or boxy sounding. It gets muddy but it has this nu-metal ish SAG that makes it sound HUGE!
The traditional Rectocab / now called Stiletto cab has more mids and is tighter / less muddy. To my ear, modern gain fills the standard rectocab while vintage high gain sounds better in the smaller cab.
Marshalls are the same size as the stiletto cab but the construction has slightly more flex so they don't pound quite as much. They aren't quite so loud but they have that traditional mid heavy rock voice. Pay attention to speakers, each model comes with different ones.
I haven't tried orange but as I understand it, they are tight and dark like mesa but since they are smaller than a Standard Rectocab, they are similar in sound to the stiletto. Someone who has one should chime in.
Mills. I haven't played through one but I have heard clips. These suckers are BIGGER than a Standard Rectocab but because of the proprietary design, they break up standing waves which results in a tight and articulate tone. Good for many styles but SUPERB FOR BRUTALZ! ALso costs a lot!
There are more 4 x 12s available so perhaps others will chime in with their experience.