From what I know my i5 ivy bridge 3317u laptop cpu at 2.4ghz is like 2.2x faster then my 2ghz c2d p7350 laptop cpu and seen benchmarks that of oc core 2 e8400 at 4.4ghz scoring similar.
So 2.6ghz is probably= to 4.7ghz core 2 duo performance. You can't really compare them as current i5 dual cores have hyperthreading and memory controller meaning more bandwidth. I assumed you are on about i5 dual cores with hyperthreading as you are on about laptop.
Thanks for your response!