peaveys are hard to beat for thrash, unless you really wanted the old school heavily boosted marshall JCM 800 tone with cranked boost pedals in the front
lot of metal bands used TWO boss super overdrives in series
if you go with peaveys, you also have two options... the roaring grind of the 5150 models or the dense and edgy tone of the ultra/xxx/3120/rockmaster family
both are amazing for thrash, but in quite different tastes
you could get great results with some of the older models, like the Triumph (which is a lot like a mesa mark III with some Peavey classic juice to it), the butcher (JCM 800 clone) or the VTM (hot rodded JCM)
those sell for quite cheap, so you could even buy two or three of them, depending on how much you wanna spend with cabinets