*Dollar rallies after Bernanke testifies to Congress. *BOJ upgrades economic assessment, stands pat as expected.
*FTSEurofirst 300 closes up 0.7 pct at 1,245.66 points. LONDON, May 15- European shares scaled new five-year highs on Wednesday, led by gains for several major Swiss stocks after a fresh fall on the Swiss franc that should continue to buoy the country's exporters.