Core i7 或 Core i5 哪個比較優?

請問Intel® Core™ i5-540M Processor (3M Cache, 2.53 GHz)
Intel® Core™ i7-640LM Processor (4M Cache, 2.13 GHz)
兩者比較哪個比較優?
Core i7 640LM 報價US$332
Core i5 540M 報價 US$257

(Core i7 640LM)
http://ark.intel.com/Product.aspx?id=43563&processor=i7-640LM&spec-codes=SLBMK

(Core i5 540M)
http://ark.intel.com/Product.aspx?id=43544&processor=i5-540M&spec-codes=SLBPF,SLBPG