This is one of those, "if it ain't broke then don't fix it" situations. Going to a bigger cam, especially a voodoo or extreme cam increases the chances of the cam going flat and eating up the engine bearings.
However, more cam would work better. I would use an old school Comp Cam 292H (244/244, 110 LSA, 0.501"), as it is a lot less likely to go flat due to softer ramps Get the cam hardened and use an oil additive (zddplus.com). Plus you don't need a split duration cam with those heads. Should make power a little past 6000 rpm in a 400 cid, 6500 in a 350.