The Core i5 Retina iMac is slightly faster than the other Core i5 iMacs, and is competitive with the Core i7 iMacs in single-core performance. However, the Core i7 iMacs are up to 20% faster in multi-core performance.
The Core i7 Retina iMac is significantly faster than all of the other iMacs (including the Core i5 Retina iMac), with at least 15% higher single-core performance and 10% higher multi-core performance.
These Geekbench results aren't surprising since all of the iMacs use Haswell processors; any performance increase is due to the increase in clock speed.
How does the Retina iMac perform compared to the Mac Pro?
The Core i5 Retina iMac is faster at single-core tasks but slower at multi-core tasks. The Core i7 Retina iMac is also faster at single-core tasks (25% faster than the fastest Mac Pro) and is also faster than the 4-core Mac Pro at multi-core tasks.
If you're considering replacing your Mac Pro with a Retina iMac then these results show it's not a bad idea provided you don't regularly run heavily-threaded applications.