The only performance gain with running stronger springs is that you are able to run higher lift with cams.
Their are many downsides to running stronger springs. From robbing potential power because of a higher load on the engine to creating extra stress on the timing chain and dampener. Comp Cams use to have a great track record with the 105's, but they've had a lot of issues this past 2 years some of their springs are now being manufactured in Mexico.
If your going with a mild setup, get the springs I pointed out along with either rockers or a mild cam like I noted with the VS cam.