2012 iMac i7 vs. 2015 Retina i5 w 1TB/Fusion?

Since you have both, you're in a better position to know if you're giving up performance for what you do than anyone else. Run some trials. It really depends on what you do with the computer.

 

It really depends on the specs you ordered but chances are the 2015 is incrementally better. It also comes with new peripherals, an improved display (again) and faster SSD storage. Seriously though, if you maxed out the graphics card on the 2012 and say you got the m380 this time around, its entirely possible the 2012 still has the stronger GPU.

 

I don't own previous version of iMac. I own late 2013 rMBP 15 i7/16GB/512GB. I just recently purchased late 2015 iMac 27 i5/8GB/2TB Fusion. The performance differences between i7(rMBP) vs. i5(iMac) to me is not really noticeable for day to day usage. If I would sit down and do comparison between the two, I might see slight different. Otherwise, I don't. especially with page, numbers, etc... they are almost identical as far as launching the app. I am sure for those who has huge Lightroom Catalog or Premiere 4K stuff will see some different. I am very happy with my iMac purchase in term of performance and cost.

 

I'm not a big benchmarks guy, but you can find results here...

http://browser.primatelabs.com/mac-benchmarks

My guess is the new system is a bit faster than your old one (I also have a late 2012 i7). The new system will also have some good features like better support for external displays (4k, ultra wide, etc), faster ports (eg. TB2), and other future-proofness. And yeah, disk reads and writes are probably 2x faster, and the RAM is faster as well. Overall, it's a pretty nice bump.

You may get a small hit when you're doing something that could leverage hyper threading... say you're running Handbrake in the background, while doing other tasks. In that situation, your old i7 might do a more efficient job of orchestrating resources. But otherwise, you may have a slightly snappier feeling system?