iMac Performance (June 2014)
When compared to the rest of the iMac lineup, the new iMac has reasonable single-core performance — it's almost identical to the entry-level quad-core iMac. Multi-core performance is significantly lower due to the lower number of cores (2 cores vs 4 cores). One interesting thing about the new iMacs is that they use a low-voltage i5-4260U "Haswell" processor (the same processor is used in the MacBook Air). Why would Apple use a low-voltage dual-core processor in a desktop machine? The answer might be graphics:
According to Intel, the HD 5000 is twice as fast as the HD 4600. Apple may have sacrificed multi-core performance for GPU performance. Given the increasing importance modern user interfaces place on GPU performance, this may turn out to be a smart decision that extends the useful lifespan of the new iMac.
I'd say Apple used an Ultrabook CPU in the new iMac to avoid shipping Intel's HD 4600 GPU in anything. No desktop CPUs include HD 5000.— Andrew Cunningham (@AndrewWrites) June 18, 2014