correct me if im wrong but the standard valve springs are pretty good, they get a bit tired after a while as all engine components do
there are alot of stock heads pushing 350rwkw and reving to 8 and past that even.
Like whats already been stated ur goin to know if theyre not working properly as valve float will show up at the top end of ur power curve on a dyno graph
as for standard cams, they too do a pretty good job up to and past 350rwkw... gains are to be had by changing them out at this stage of tuning though some people are content with just some aftermarket cam gears with a bit of adjustment