It is unfair to compare the C2D with i7 actually. For 1 thing, the i7 have 4 true cores that makes it superior than the C2D just in terms of having more core to do parallel processing. And it have hyper threading that even jack up the performance lead even against other quads processors.
New processor architecture often, if not always, produces improved processing power. This can easily be seen. Take an Intel Pentium D 960 (dual core at 3.6Ghz w/2x2mb l2 cache), it receives a passmark score of about 1000. The Core 2 duo E7500 (2.93Ghz dual core, 3mb L2 cache) score about 2000 and does it with 600Mhz less clockspeed and 1Mb less cache. Both of these get beat by the low end I3-530 (2.93Ghz dual core, 4mb L2 cache) which score about 2700 when its not overclocking itself.