In almost every circumstance, April performance means little or nothing. Last year's April stars included Placido Polanco, Brett Wallace and Sam Fuld, each of whom would see their numbers come crashing back to reality as the season wore on. Over the course of 100 plate appearances, nearly any player can produce good or bad results.
However, there are some statistics that have some predictive value, even in limited quantities. Velocity, for instance, stabilizes extremely fast, as you'll never see Jamie Moyer fluke his way into throwing a 95 mph fastball. On the offensive side of things, the closest equivalent to pitcher velocity is contact rate.
Adam Dunn swings and misses a lot, while Juan Pierre puts his bat on the ball nearly every time he swings. You don't need to see many games before it becomes clear which guys make contact regularly and which guys do not. In fact, contact rate has the strongest year-to-year correlation of any offensive metric, and it is the most consistent skill possessed by any hitter. Sustained significant changes in contact rate are rare and can generally be identified much faster than a change in some other skill set.