For Guitar, I totally agree with using PA amplifiers and cabinets loaded with ProAudio speakers, provided you are using a high-end guitar processor such as Fractal Axe FX, Avid Eleven rack, Roland VG99, etc. Virtually all guitar amplifiers include coloration such as tone controls, distortion/overdrive, presence, reverb, that would need to be set flat, neutral, or OFF. These features become redundant and even unwanted.
Today's processors do it all, including dynamics, delay, pitch-shifting, you name it. The guitar amplifier becomes nothing more than a power amp, neutral in all respects. If every patch you command from your pedal has custom settings designed to fine-tune that sound, why add further color from your amp head and speakers?
Now, let's talk about speakers. The whole idea behind a "guitar speaker" is to reproduce the range of frequencies a guitar is capable of. In addition, a design that allows for a desirable "break-over" point, both resulting in a characteristic rock&roll tone, and tolerating being overdriven without damage. ProAudio reproduces almost exactly what you feed it at a broad range of volume levels. The average Celestion, Eminence or Fane speaker, etc. is rated at 75 to 200 watts RMS and is intended to be overdriven, while ProAudio (for a 12") would be best specified at around 500 watts, and should never be overdriven. Generally, they offer a usable frequency range of 40-4000hz. The Roland VG99 processor is capable of dropping you down a full octave. Although you might not use those patches very often it would be nice to have a system that can support frequencies low enough to enable you to hang with your bass player.
The bottom line is: If you must have a true "vintage" sound, go with analog stomp-boxes, tube amps and a good sealed cabinet designed to give you that "Marshall" sound.
Otherwise it's digital all the way!