Return Single Value from Mutliple Criteria

Hi

I need to lookup and reference 3 separate criteria, then return a single value based on that criteria. I have been using a Sumproduct formula , =SUMPRODUCT(--('Data 2007-Current'!$AD$2:$AD$1002=$B21),--('Data 2007-Current'!$AH$2:$AH$1002=C$5),--('Data 2007-Current'!$AI$2:$AI$1002=$B$5)), but it is very very slow to calculate, so I am seeking a better option.

The criteria is unchanging and will be the same based on the data I'm extracting:-

NVT Consulftant (A Persons name)
Month year (MMM-YY) - A date
Category (the categoy of work)

The source data for the lookup is contained within yearly tables and the layout/design of each table is identical. There are 4 source data tables altogether, 2007,2008,2009,2010.
The value found is then going into a separate Data sheet as Chart Data. Can anyone help?
Thanks