Just installed OWC 8 GB 1333 ram on my otherwise stock, base model 2011 13" i5. Thought I would share the geekbench scores (before and after) FWIW:
MacBookPro8,1 4GB Score = 5927
MacBookPro8,1 8GB Score = 6034
I thought the performance improvement might be psychosomatic, so I created my own little benchmark test, an action (macro) made up of series of Photoshop filters applied to three different files of varying sizes, and timed them before and after the 8gb upgrade.
I restarted Photoshop after each test to ensure a clean scratch disk.
13" i5 2.3
Before:
File 1: 198 sec.
File 2: 8 sec.
File 3: 79 sec.
After (8gb RAM):
File 1: 176 sec.
File 2: 2 sec.
File 3: 30 sec.
File 1: 960.3 mb
File 2: 72.6 mb
File 3: 338.6 mb
Not very scientific, but it put my mind at ease: I didn't blow a hundred bucks just to make myself feel better.
I was surprised that the performance increase was so little with the largest file, but it makes sense now that I think about it: the PS scratch disk may be taxing the RAM even at 8gb with a file that's nearly a gig.
In any case, most of my work falls in between the second and third files, which both saw significant speed increases.