I disagree. I think the 4" might make a little more sense if you aren't going for SERIOUS power. The 5" won't hurt, except in the wallet, but it will be kind of tight to fit. Especially where the downpipe passes between the bellhousing and framerail. My 4" rubs the spare regularly also.
Of course if you get bit by the bug and go over about 350 hp, you may regret not going 5". And the 5", I must admit, sounds mighty mean!
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