I maxed it out at 16GB, 4GB per stick. Regarding your question, it will still work but a lot of us prefer to run ours with 4, 8, 16, 32 GB increments. Unless, I'm mistaken.
I am getting ready to do upgrade my 2010 iMac as well. An idea for you is to look at eBay for people selling their OEM ram for their iMac/MBP. There are a few 4gb (2x2gb) on eBay that are going for around 30, which gives you 8gb for super cheap.
I maxed it out at 16GB, 4GB per stick. Regarding your question, it will still work but a lot of us prefer to run ours with 4, 8, 16, 32 GB increments. Unless, I'm mistaken.
I'm thinking of upgrading the RAM as well. So how did you go? any performance difference? mine is 2010 model and getting slower when using Photoshop and Adobe software.