In XL 2007, I have a sheet with between 100 and 30000 rows at any one
time, across 40+ columns. Many have formulae in them.

The code takes a list of up to 10000 unique 10 digit numbers from
another reference sheet and puts them in an array. Each row of our
target data is checked against the array via 2 'for' loops.

A positive check results in some existing data in the target's columns
to be changed to alternative text.

A comment field up to 60 chars large receives a 5 alpha comment
appended to existing comments.

No objects or shapes are referenced. No pagesetup code is used or
performed prior to running the code (a recognised boo-boo for XL 2007)

Display update is suspended. Calculate is suspended.

However, if the target data has more than several thousand rows to
parse, the code grinds to a near halt. I can tell this because I have
a progress bar which starts very fast then slows right down and can
eventually even reach near zero progress. If I can break the run in
time, the sheet becomes molasses to negotiate. Other sheets it the
same workbook are fine and responsive.

So I check the blank cells for hidden data or formulas. None.
There is no new data at all, only replaced data. Update and Calculate
is restored. Formulas recalculate. Save the book and reopen in new XL
session. Still molasses. Book has doubled in size.

Thoughts:
Haven't been able to run in XL 03 to test if it's a 2007 problem.
There are OnChange events in the workbook, which I assume suspend
during the running of my code. In any case, why does the book still
get slulggish save/after reopen, etc.

Equipment: Core 2 Duo, 2 Gb RAM. XPSP3, XL 2007 SP2

tia,
I.D.