I am tired of people saying that the F50 can't do metal!
If you use an open back cab, then yeah, it can do rock and blues real well. But, how many metal guitarist use an open back for metal tones!??? Get yourself a good extension cab, and you will get the low mid chunk you are looking for. I use a Mesa Thiele extension cab with custom 90's. It has a ton of chug, and there is a lot of definition, especially with the contour mode on.
The F50 has a sh!t of gain/distortion. Once you get past 2 O clock on the gain, your sound turns into distortion mud! Hell, any amp with that much gain turns into mud. At that point, the question is, "do you hide behind gain?" Is your technique and tone so sh!t that you have to blast the gain to hide flaws in your playing?
I use 9 o clock on the F50 gain, with the master level at 11:30, and I get an incredible chunk (open & close back cabs). It will give you a great "rock sound." ala priest, vh, crue, etc. Once you get to about 11 or 12 o clock on the gain, you will have a sh!t load of gain with plenty of defnition. It will get that death metal & nu-metal sound with ease, especially with the close back cab. After that, it turns into distortion mud, just like any high amplifier (recto, mark, uber, diezel, engl).
If you want nu-metal, "recto" sounds, the F50 won't give you those sounds. If you want over the top F50 distortion, no problem! The contour mode has a tone all its own. No mark series, no recto, no stilleto; just F50 tone bliss. I will try and post some metal clips once I convert files to MP3 & figure out how to post them.
I hope this helps