Macbook Pro Intel Core i5 vs i7 enigma

I have a macbook pro 13' with a dual-core intel i7 processor that reads 2.5 GHz that I bought brand new in 2017. I also have a MacBook pro 13' with a dual-core intel i5 processor that reads 3.1 GHz for work that is also from 2017. Why would an i5 read a faster processing speed than my i7 if they're the same age and same computer? The graphics on my i7 says it is an Intel Iris Plus Graphics 640 1536 MB meanwhile my i5 says it is Intel Iris Plus Graphics 650 1536 MB. Are the graphics cards not the same because the i7 says 640 and the i5 is 650? They both have 8 GB of memory with 250 GB hard drives.