Considering how old the processor is, I doubt that faster RAM would make an appreciable difference. With most phones and cameras shooting HD (and 4k) now, there is no way a 6-year-old iMac will be able to keep up for video editing.
Mine:iMac 5k (4.0/24/1TB Fusion/295X), 12" MacBook (1.1/8/256), iPad Air 2 128GB WiFi, iPhone 7 Plus 128GB
Hers: 15" Late-2011 MBP (2.2/16/480 SSD), iPad Air 16GB WiFi, iPhone 5c 16GB
Home Server: 2010 Mac Mini (Core2Duo/8GB) with 14TB attached storage
Other Stuff: Apple TVs, Airport Expresses for AirTunes, ASUS 802.11ac routers