The minimum investment of $10K and $100M, respectively.
if available through employer's plan, is VSMPX a better choice?
I hold a little bit of VSMPX through a former employer. As I understand it, the two funds are are exactly the same except for the expense ratio (0.02% versus 0.04%). At USD$200 per million invested per year, you are unlikely to notice the difference, but I know of absolutely no reason not to buy VSMPX if your employer will let you.