I am looking to replace the stock speakers in my B-52 4x12 cab and would like some helpful input. I play mostly metal and hard rock. I want to do an x-pattern and I'm currently looking at eminence texas heats, swamp thangs, and man o wars. Also, most celestion speakers are out of my budget.
Consider the specifications of the speakers that you are looking at.

The low E on a 6-string guitar is at 82.41Hz. For a 7-string, the B is at 61.74Hz.

When a string vibrates, there are several octaves also ringing in unison with the fundamental pitch. These are called harmonics (2nd, 3rd...). When you pick a low E, you're actually hearing the composite wave produced by 82.41Hz + 164.82Hz + 247.23Hz + 329.64Hz... and so on. The amplitude of each harmonic is what "tone" is.

The bottom line:

Frequency Response:
82.41Hz - 20kHz If using a standard tuned 6-string
61.74Hz - 20kHz If using a standard tuned 7-string

100dB+ for 1W@1m Higher sensitivity = louder at the same power input.

Match the cabinet's impedance with your amplifiers rated impedance for best stability and power transfer. If your amplifier is rated to drive 8Ω, then your speaker cabinet needs to total 8Ω.

Four 8Ω speakers can be wired to achieve a total of 8Ω.

Good luck and if you have any other questions, I'll try my best to help. It's tough to choose what's the right choice on a budget, but there are many solutions.