4x is a tad much, though nobody would deny the newer models are faster in many ways... especially with faster buses for peripherals such as hard drives, faster video subsystem, etc...
http://cpuboss.com/cpus/Intel-Core2-Duo-T9600-vs-Intel-Core-i7-3615QM
(interesting differences; did not know the T9600 had 6x as much on-die cache...)
http://www.cpubenchmark.net/laptop.html
(here is where the ~3.5x claim tallies up, but static benchmarks vs real life usage are often considerably different. The CPU is 3x faster but it doesn't follow suit that the OS and apps will run that much faster, as the previous benchmark alluded to. Depending on how much L1, L2, and L3 cache exist on the CPU die, and the type of application being ran (3D rendering vs database manipulation), one CPU won't fare better than the other by the same amount...)
http://en.wikipedia.org/wiki/MacBook_Pro
(has the whole list of CPU model #s; finding those and comparing online to get ideal performance variables is only a small matter of time.)