Went back to 2.56. Tried 2.57 for a week, CPU is almost maxed out at all times.
I've 80 torrents, about 4 downloading, 8 uploading; 4 channels, including Channel X and Torrent Cache which are big.
But my payload is not the problem, shutting channels off didn't help.
As soon I rolled back, CPU went back to normal, about 10%.

Running Win7-64 SP1 Home Premium, 2.5GHz i5-2450, Intel C600 notebook chipset, nVidia Optimus.
8GB DRAM, 60GB SSD SATA2, 1.5TB USB drive.