"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Core i7-Based 27" iMac Benchmarks Show Significant Improvements
Various Geekbench and Cinebench scores for the new i7 iMacs have been reported. The best visual representation is provided by this blog entry at Timon-Royer.com which compiled the Geekbench scores across all currently shipping iMacs:
Longer bars are better with the new i7 iMac (green) performing significantly better than the Core 2 Duo 21.5" iMacs. The i7 even represents a sizable (35%) performance increase over the i5 model and costs only $200 more. In fact, the i7 iMac benchmarks compare favorably to 2.93Ghz Quad-Core Mac Pro which costs significantly more.
Update: Timon Royer has updated his blog post with a new chart correcting a minor error on the Core i5-based iMac data and adding results for the latest Mac Pro models for comparison purposes.