While higher resolutions and framerates normally go hand in hand, its the bitrate of the video/audio which will define how much data is written. For example a 720p @ 5fps encoded at 1mbit, will write twice as much data as 1080p @ 2fps encoded at 512kbit. The resolution, the frame rate and the bitrate affect quality but only the bitrate of the stream affects size on disk and IO requirements.
Ive got a WD green SSD on USB on the pi, but when it came to it I did the calculations and released i'd be thrashing the small drive with writes and bought a WD purple and 12v powered usb adapter so it can drive the engine knowing the drive is designed to be continuously spinning and doing continuous writes instead. Its only been 2 weeks, but so far, so good.