I bought a FB straight 4x12 after playing one that a guitarist from my band's sister band let me borrow for a bit. That thing was so articulate, warm, punchy and vibey.
P50E's are great once broken in, but that break in takes a very long time, like 100-300 hours, and I sold my brand new FB because of that.
I also built a 16 ohm FL 4x12 with 90's "UK" V30's and T-1221 modern Chinese Greenbacks ala Friedman Top/Bottom style with Aiken wiring (V30's series bottom/GB series top parallel at the jack) and loved that cab. Ultimately, I can hear non-Mesa spec V30s and reject it the same as Steve Fryette did which inspired him to create the P50E. There was something non-musical in the Greenies too. Ah, the cursed sensitivity! Ugh!
My advice: Get a well used and broken in FB cab, and if you don't like it, build your own cab with used, well broken in speakers and do a series of experiments until you find exactly what suits your taste.
That said, to date, nothing beats my '03 OS Mesa 4x12 modded to single jack S/P wired Aiken style with Marshall Sound Runner 10 ga. and a 4" thick slab of acoustic foam on the back panel. If you're a 16 ohm guy, just replace the speakers with T-4416's. There's just something holy about those cabs. If you play standard tuning, traditional size will suit, if you play lower, OS gives the "displacement" for the lows to be muscular and open.