4 x 12 vs 2 x 12: both are of the same volume, but the 2x12 is slightly tighter, the 4x12 has more bass and fills the room MUCH more, and sounds more powerful and able to handle higher volume easier.
Slanted vs Straight: not much difference - if slanted, more highs get to you and fill the room even more.
Front loaded vs Rear Loaded: front loaded is said to be tighter and have slightly less bass, but honestly, i havent noticed any significant differences.
Open back vs Closed back: closed back has much much tighter bass responce, and more bass, but doesnt fill the room as much as an open back - but the tone you'll hear from a closed back is more pure because sound is comming from just one direction
Value for money manufacturers: carvin cabs are good for the money i guess, but i dont think id buy one - invest in a quality manufacture so you wont have to flip out the cash for a better one later - but if you have to get a cheap one i guess...go for avatar
Top Quality Cabs: vht, bogner, framus, mesa (all of which are strong recommended)
Speakers: it is all to your taste! for a mark iv, ive heard the vintage 30s to be used often, but i guess they are used often for everything. im betting a bogner uberkab would sound awesome through the mark iv - has g12t75s and vintage 30s - so maybe a combination of speakers would be good. greenbacks are said to sound woody and warm, but in the cobra cabinet they are said to be very dark and tight...so you can only decide so much based on the speaker alone - the cab has a lot to do with it.
