Sometimes, slow and steady really do win the race. EBay (EBAY) is among the top big-cap stock winners this year, trudging steadily up its 10-week moving average to a gain of as much as 75% this year. Stocks that join IBD Big Cap 20 (featured every Tuesday) typically move more slowly than their high-growth counterparts. It can take them a long time to form a base, but they tend to be less volatile. That's because their high market capitalization --