What year/version Imac?
Happy camper with iMac 27" (late 2012), 32 GB memory, 2 GB 680MX Geforce GPU (CUDA driver Version 5.5.25), 3 TB internal fusion drive, 12 TB external storage via thunderbold connected Areca Raid6.
I mainly work with < 2K aka AVCHD material (H.264), burning to BR, converting to Web, etc.
PPro CC (as also the rest of CC) runs without problems in parallel with Logic Pro 9, Wavelab, Cubase and approx. 100 video and audio plugins (e.g. suites from Redgiant, Waves, Plugin Alliance, Native Instruments, Vienna Symphonie Library, etc.).