Should I get out of Vanguard 500 Index Fund (VFINX) and put it into Vanguard Total Stock Market Index (VTSMX)?

I'm not looking to diversify per se or leave Vanguard Funds, just chase a better long-term return. The data says that VTSMX trounces VFINX over 1-, 3-, 5-, and 10-yrs - the only difference comes at since inception: 10.62% for VFINX vs 8.47% for VTSMX. So, what am I missing? I don't want to do the ETF thing, either, so don't bring that up and I don't have enough invested (yet) to go with Admiral shares.