3.5" turbo back is a bit ecessive. Which GT35 are you going with? How boosted? It's not generally recommended to go bigger than 3" unless you're going for a pretty excessive power number. Stick to 3" and any muffler you want. Unless you're trying to squeeze as much power out as possible, go for whichever one suits you best. Loud, quiet, rubble, or rattle. Heavy or light.
1995 BMW M3 Turbo - Dakar/Black