Small-cap stocks were largely buoyant Tuesday, and one of the biggest winners was Cambridge Display Technology ( OLED). Shares of the Britain-based company soared some 88% after Japan's Sumitomo agreed to buy it for a gigantic premium of $12 a share, or $285 million, in an all-cash deal that will likely close during the third or fourth quarter. Cambridge Display shares traded up $5.43 to $11.58. Midwest Airlines ( MEH) also gained on M&A news. The Wisconsin-based company, which has been pursued by Airtran ( AAI) since late 2006 in the face of repeated rejection, now says it will begin discussions with the discount airline. AirTran's current bid is for around $15 a share in cash and stock. Midwest also says it has recently attracted interest from "other strategic and financial parties" that it intends to explore. Its shares rose 12.9% to $14.23 in support of the Russell 2000, which lately climbed 4.69 points, or 0.6%, to 788.92. The S&P SmallCap 600 similarly gained 0.7% as member Headwaters ( HW) blew away fiscal third-quarter expectations. The Utah-based company, which sells products and services to the energy and construction-materials markets, said earnings leapt by 40 cents a share from last year to 98 cents -- double the amount analysts were seeking. Revenue, at $336.3 million, was also well above the consensus. Shares surged 13.4% to $16.99.