New iMac or wait for Mac Pro (for Lightroom and occasional Photoshop work)

My 2008 Mac Pro (3,1) just died. I have a Macbook Pro as well that I am using as a backup, but I'd like to replace the Mac Pro with another desktop. I'm not a pro, but I do quite a lot of photography work on the computer and I have an appreciation for speed and performance. That said, while I used to use Photoshop a lot and work on big files with many layers, I'm finding that I hardly ever do that anymore. I use Lightroom almost exclusively now. I don't do any video editing or gaming.

For the iMac, I'd get the 3.5 Ghz i7 with 512 GB SSD and 4GB GTX780M Nvidia. I'd buy with stock 8 GB of RAM, but buy the 32 GB upgrade from OWC. I would then get a DataTale 4-Bay Thunderbolt enclosure in JBOD configuration to hold my photos (on a 4 TB HDD), backup (4 TB HDD), ACR scratch and LR catalog (480 GB SSD) and Time Machine (4 TB HDD).

I've heard the recent iMacs are quite snappy with Lightroom and even basic Photoshop work. Can someone confirm this? If it's fast enough, I don't want to spend the extra money on the Mac Pro.