Putting a huge cam in an engine does not necessarily mean you will gain huge power. It's better to create an engine where the components are synergistic. Case in point: check out the link below. It's an article using an LS2 engine comparing various cams and heads. An LS2 head flows similarly to an LS6 head, which is significantly more than your 5.3 head.

With the stock cam (204/211 0.525 116) and heads, the engine made 400 HP.
With a 218/220 0.570 114 cam and stock heads, it made 494 HP.
With a 232/236 0.600 114 cam and stock heads, it made 500 HP.

Even though the last cam was much bigger, it only made 6 more HP. The heads just couldn't flow enough air to support the cam. Your heads will give up sooner, probably in the 220-224 range. Add nitrous to the mix and the problem gets worse. That's why I suggested cams in the 214-216 range.

It's always better to pick a cam that works in your engine, not one that sounds good when you talk to your buddies.

LS2 engine tests stage one and two - cams and heads - GM High Tech Performance