I don’t think it is possible to get the consumption of T450s on X220.
The T450s generation (and the generation before it) use ULV processors (ultra low voltage).
The processors used in the T450s generation have a TLP of 15W.
The processors used in the X220 generation have a TLP of 35W.
On the flip side, the processors in the X220 generation (and in the next generation) are powerful, which is a good thing if you need the power and if you have the laptop plugged most of the time.