The Rivera isn't actually super gainy. It is a high gain amp but at max gain it doesn't have anywhere near as much as something like a Rectifier. The CL is probably a better option for metal stuff. I liked the Rivera I had well enough but ended up looking for something a little tighter. I did love the low mid focus on the Rivera though.
I had a CL50, good amp, but after having a CLX, I much prefer the 100w power section with the VHT's. I'd look for a CL100 or an Ultra Lead if you can afford it.