If you have a "decent-sized" amount the place for it is almost certainly NOT the C fund.
I have to agree with that. The success (or otherwise) of any lump sum investment is determined largely by the price at which you buy. It's far better (imho) to smooth out the natural volatility of most funds by making regular contributions - monthly or quarterly if possible. There is a small chance that you will miss out on great returns but it does significantly reduce the chances of getting burned. Depends on your appetite for risk I suppose.