Excel2003 ...

My understanding is ... an array "Index/Match" Formula calculates faster
than a "VLookup" Formula ... If so, then I would like to use "Index/Match".
Also, I often do use "Index/Match" as the Index can be either R or L of
target cell.

Issue ... with 2 Cols of 40,000 records ... Index/Match Formula fails to
copy all the way down the 2nd Col ... It seems to fail @ about 20,000 records
down the 2nd Col (one clarifier ... I am on the same WorkSheet ... adjacent
Cols)

Above said ... Am I up against an "Index/Match" constraint here ... or ...
as is generally the case ... Is this an oversight on my part?

Please enlighten me ... Thanks for the guidance ... Kha