Single 3 is good to around 500. 3.5 can support more.
A friend of mine has made 825whp with 3.5" exhaust. Not saying it wouldnt pick up power with 4" but it made close to 1K crank with single 3.5.
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3.5" will be fine. Ive ran overkill exhaust and there was minimal difference from a set up closer to stock.