I could tilt the speed by not having memory sticks in pairs, get one a better GPU or SSD.
If you feel it's just the CPU, you can compare that at CPUBOSS.
Processor 1 - Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz
System Model 1 - OptiPlex 9020
SMBIOS Version - 2.7
Processor 2 - Intel(R) Core(TM) i7-2600 CPU @ 3.40GHz
System Model 2 - OptiPlex 990
SMBIOS Version - 2.6
other all details are looking same
which one i have to choose