Using the stage 3 stroker kit to suit V6 Ecotec and adding steel crank how much does that increase power range to?

You would be looking at at least 700rwhp. In saying this though you would want to upgrade the conrods to a brand such as Carrillo. To give you an idea as to what's possible, please check out the link below:

http://forums.justcommodores.com.au/mace-engineering/164956-513rwkw-v6.html