Is iMac 2011 (SSD) to newer iMac substantial upgrade?

[musiclvr]

I currently have a 27" mid-2011 iMac with the following specs:
Processor: 3.4 GHz i7
Memory: 16GB
Graphics: AMD Radeon HD 6970M 1024MB

About 2 years ago, I bought a Samsung 840 EVO 500GB Internal SSD with an enclosure, and now I use that as an external SSD via Thunderbolt to run the OS and all applications. The iMac hard drive is used for photo and music storage.

I run quite a few programs at a time. I do a lot of web browsing, photo editing (Photoshop, Lightroom, etc), etc.

I've been going back and forth debating on whether I should upgrade. Obviously the 5K screen would be the biggest upgrade. Performance wise, would I notice a substantial difference if I upgraded to one of the 2015 27" models?

 

[tiktok]

I have the exact same machine and I love it! I just repaired mine with a new GPU (that 6970 is prone to heat death, don't know how you use yours but mine died after a day rendering H264 clips).
The advantage of the 2011 mac is that you can actually swap said GPU if it fails and with a bit of tinkering the HDD/SSD etc too. Mine hat a 4TB HDD plus a 500GB EVO850 as a fusion drive.

Obviously if you can afford it the 5k display is a hell of an upgrade for photo editing but anything else.. (I edit medium format scans with 50-90 megapixels on mine, CPU is good enough for that)

[EDIT] That said, I'm not sure - do the current iMacs feature PCIe SSDs? If so, those are fast.
The one in my macbook air is twice as fast as the 850EVO