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I see your point, but I drive an average of 3000 miles a year, so it would take 67 years to go 200k . Considering that, either option is viable. Also I'm looking at reasonably mild cams with lift at or under .600 so I don't see any reason why the built setup would be life limited. Either setup will be 10.5 to 11.0 static compression ratio.
PWC clearance is greater on a forged piston. higher rpm and less ring tension coupled would greater clearance typically means more oil being burnt, but, you have a motor that can take a lot more bang
if you're staying with a mild under 600 lift cam and not revving over 6600 i would stay with cast. they are quiet, live forever and don't burn oil.
depending on your hp goals you might be able to just use a late model ls1 bottom end with some ported 243 heads and have a strong street car
440 hp at the wheels has been done more than once with a stock bottom end, also would be an inexpensive build
I think you have made a great decision by ordering a TSP 408 Long block with PRC 237 heads and Ed Curtis cam. Really hope you will have a great experience with this new engine.