I'd argue why not Exodus instead of Testament? There are too many thrash bands that deserved to be part of the Big 4 but still didn't make it. Testament is no exception despite their rather groundbreaking 'The New Order'.
People sometimes refer to Metallica, Megadeth, Slayer and Anthrax as the First Tier of the Big 4. That being said the Second Tier would consist of Testament, Exodus, Overkill and a 4th one of your choice (mine would be Heathen but some would prefer Kreator, Vio-lence or maybe Death Angel...hell even Flotsam & Jetsam could make the list). It's a matter of preference.
As for the questions on Alex Skolnick ask Shaun...he's probably the best person to ask.
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