Which dual core? Which i7? What will they be used for?
There are many different models to choose from or compare.
Usually, its more a question of what's the best CPU you can afford to buy. And the answer is usually something that's 'good enough'.
Generally, the Core i7 i7-920XM (3.06GHz - 3.2GHz, 4 core, 8 threads) is probably the better mobile CPU.