VBA code for formula

Hello everyone. I have followed many of the suggestions that were given to me w.r.t an automation I am trying to develope. But most resulted in fails.

I am using the following excel formula within a worksheet with approximately 20,000 records.

=IF(OR(E6="PV",E6="PV_C",E6="DC_FUT_B",E6="CETES"),IF(ISERROR(VLOOKUP(I6,[Illiquid]RVFL_C_Step_C!E:E,1,FALSE)),E6&"_1",E6&"_2"),"")

Originally I was going to paste the data necessary to compute the formula into the worksheet, and allow the formulas to automatically "update" after pasting. This is causing the macro to crash [ white screens, not responding etc.] This formula resides in column AC.

Is it possible that an actual VBA code to compute the formula as oppsed to an excel formula in the sheet will speed things up? Maybe a different excel formula? The Find_Method?

Any suggestions? I do not want to use access.

I can post the entire VBA code for the project if necessary.