What do you mean slowdown? The difference will be negligible. Stop looking at geekbench scores. A 2012 27" would be ideal if the screen improvements really are significant. The 2011s were close to $300 off refurbished, so it can be a significant savings. Aside from possibly opening and saving files, you'd benefit way more from ram. These applications can just cache to ram instead of dumping it to disk. I also have yet to see how they manage data, especially with things like scratch disks. It's not even necessary to go to 32GB. Add 2x8GB sticks to the existing memory. Test it once it's added. If that basically takes care of everything, you're good. 32 could be usable if you're working with really large files with layers, especially if you have lightroom open simultaneously.
The slowdown with Adobe apps can be complex. They tend to interfere with spotlight at times, especially when it's indexing. It also tends to cache a lot of data when saving large files with compression (enabled by default). This means if you're saving to the same drive as it uses for scratch data, it will slow to a crawl with either drive type.
Last thing would be PS and LR are both OpenCL (I think LR has OpenCL leverage). Neither uses CUDA. I'm positive of that. After Effects and Premiere leverage CUDA. Those would require an NVidia card for certain functions. With the two you mentioned it's irrelevant. I thought I'd get that out of the way in case someone mentions it.
