I don't think it would be quite that simple. The $1.2M pension equivalent you calculated would not be available at the beginning to earn int, divs and CG's. That is, the $1.2M up front would be more valuable than $40k/yr for 30 yrs. And you'd have to consider whether the pension was COLA'd or not.
Per a couple FireCalc runs (default values) I just did:
If you have a $40k COLA'd pension plus a $500k FIRE portfolio, the amount you could withdraw, inflation adjusted, for 30 yrs and just achieve a 100% success rate is $57,947. Based on the $500k FIRE portfolio alone, that would be a SWR of 11.5%.
With a non-COLA'd pension and everything else held constant, the withdrawal could be $38,577 which would be an SWR of 7.7%.
It's hard to overstate the value of a COLA'd pension! That's why some of our forum members have been either delaying SS or paying back and restarting SS.
Getting back to you specific question, FireCalc used to specify the SWR (or at least the WR) of the withdrawals you specified. And I believe these figures were based on the FIRE portfolio amount exclusive of other income sources. So, for folks with pension, SS or whatever, WR's well over 4% were possible. Somewhere along the line, I noticed this feature was removed. So I look at FireCalc as a historical backtesting of a spending plan that includes FIRE portfolio withdrawals, SS, pensions and all other sources of retirement income you specify. I don't think it makes sense to try to assign a lump sum value to ongoing retirement income sources in order to determine an overall SWR.