Are these specs overkill for music recording/video editing?

Those specs are perfect for the iMac, and you won't have any problem making high quality recordings because it's the best iMac you can buy now. The only thing you can have problems is the memory, but you shouldn't buy your iMac with more memory, because you can buy it later from OWC or Crucial and save money. Probably 8 GB of memory won't be enough, but apart from that, it will work without any problem

You don't really need the i7 or 2 GB VRAM GPU for audio recoding, but seeing that you mentioned video editing, you will need these.

You could save a little by only going with the 1GB VRAM GPU, instead. This GPU would be alright for video work, too!

Don't forget to budget for the 3-year extended AppleCare warranty. You will need this.

You can purchase and register for the extended warranty any time within the first year of free AppleCare.

Good Luck!

iMacs have a removable graphic card, but Apple only allows you to install the same graphic card. If you install a different graphic card on your iMac, you will void the warranty, so you mustn't replace the graphic. For your uses, the 21'5-inch iMac could work, but you could want a better graphic card, so I think that the 27-inch iMac is a better computer for you

For the use you want, 16 GB of memory minimum. You may work properly with 8 GB, but you will probably need 16 GB of memory to continue using your iMac if you want to run more applications different to Logic at the same time

When I say 16 GB, it's because I want that you save possible problems in the future, because Logic runs with 8 GB and 4 GB, but you want also to use your computer to video editing, and here's where you may need all of that memory. Also, your computer will work for a lot of years with that hardware and amount of memory

Totally agree with mende 1 on this.

The 27 inch model is best for what you want to do.

Also, for video editing, you really need the fastest CPU and as much RAM as you can afford.

As I stated, either the 1 or 2GB VRAM GPU will be fine for video work.

If you decide to delve into doing video work and editing, I would, also, recommend at some later date, purchasing a couple of ext. USB 3.0 or Thunderbolt hard drives to assist with the workflow.

Having raw video footage on external hard drives leaves the iMac's internal drive optimized for doing the actual software video tasks by not loading up the internal drive with lots of raw, high GB video footage.

You can, also, store audio projects, iTunes and iPhoto libraries on ext. hard drives, as well.