I'm saving to buy my first 100 watt tube amp (yay!) and want something that has a killer metal tone. The two I'm looking at are The Rivera Knucklehead Tre and Kerry Kings signature JCM 800. They're both priced about the same used and I can't test any of these amps out because nowhere near me can I test one and I can't seem to find any decent reviews online.

I mainly write and play thrash but I would like versatility to other types of metal as well. Do any of you have either one of these? If you do, How is it?
Jumping on dat gear sig train.
PRS Hollowbody II / BKP Warpigs
Strandberg OS6T / BKP Aftermath
Strandberg OS7 / Lace Poopsticks
Skervesen Raptor 7FF / BKP Warpigs
Skervesen Raptor 6 NTB / BKP Juggernauts
Hapas Sludge 7 FF / Hapas Leviathan
Anderson Baritom / Motorcity Nuke BKP Sinner Anderson H2+
Warmoth Baritone / BKP Piledriver
Ibanez Rg2120x / BKP Nailbomb

Blackstar ID:Core Beam
Any reason why just these two?

I'd add Mesa Mark, TC and Recto to the list, Fryette Sig X, Orange Rockerverb, Randall Thrasher, Satan, Engl...just to name few.

Also the JCM2000 is not far departure and with overdrive might land as a contender as well.

How many watts do you need? If you don't play much a 20-30 watter might do. Actually big rigs are not as popular...
I opened up for Hammerfall and our band actually had bigger amps than they did.
+1 on the Rivera Knucklehead KTre or KTre Reverb.  I got mine for $650 and $700 via CraigsList about 5 years ago and both have awesome Cleans and more Gain on tap.  

Pass on the plain Knucklehead 100 (discontinued but cheap at ~$450) unless you just want a Clean platform for pedals. The KR100 has a built-in Reverb and cost just a tiny bit more.
Well, if Slayer is your thing the KK model should be a good choice. If Kerry is to be believed he designed the amp in mind that if he ever looses his gear on tour he could just walk in guitar center and get his exact tone out of the box with this amp, no EQ pedals or boosts or anything needed.

But is it better than Knucklehead, I have no idea.

ESP LTD F-50 + Tonezone
Cort EVL-Z4 + X2N
Cort EVL-K47B

Marshall Valvestate 8100
Randall RG1503
Bugera 333
Peavey Rockmaster preamp

Line6 Pod X3
Ktre for sure.
Ibanez UV777P
Ibanez RGD2127FX
Ibanez RG3120TW
Ibanez RGD7321
Ibanez RG6003FM
Ibanez SA160
Jackson Slatxmg3-7
Baron Custom Amps K88
Rivera Knucklehead TRE
Fryette Sig: X
Randall RM4 /w Modded modules
Mesa 4x12
Bogner 4x12
Peavey 4x12(K85s)