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........... GM is undoubtedly very conservative in their tuning (as we've seen F-cars and Holdens make an additional 20-40hp from a tune) and I think the presence of VVT only compounds that.
I'll second that,
when Holden standardized the LS1 engine production (LS6 intake and '965 camshaft) from 2002, the rated output grew from 330hp to 380 over two years just in different mapping.
Ya valve springs are a MUST do. Pushrods are optional but im replacing them. As for springs? Considering the large valve size and high rpm range dual springs are what I recomend.
Patriot Golds are my choice. Great spring, Great value