If you could sort both sheets by the column  you're checking, your loop
wouldn't need to cover the whole range, would it? That would give you a
lot more speed. But I thnk once you have your value  from the first
worksheet (if it's sorted, then a simple Do...While should do the
trick), you shouldn't need to loop  through the second; a simple .Find
command should do it more easily and far, far more quickly.

I meant to say - since you'll have multiple matches - follow the .Find
with a Do...While wrapped around a .FindNext.

whenever I deal with big  (long) XLS tables I use Filters rather than loops,
which is extremly fast. Additionally, disabling screen updating will
significantly improve execution speed. In your case it looks like the
autofilter's "custom" function (or the advanced filters) should work great.

Here is an extract of some code I use in one of my macros using the custom
autofilter:

Rows(1).Autofilter
Rows(1).Autofilter Field:=TRSC, Criteria1:=">=19", Operator:=xlAnd, _
Criteria2:="<27"
Range(Cells(2, PQAC), Cells(2, PQAC).End(xlDown)).Select
Selection.Replace What:="*", Replacement:="9999999999", LookAt:=xlWhole

This filters the data in column  TRSC for values  between "19" and "27". Then I
select the column PQAC and replace it's value  by number "9999999999". rather
than replacing the value, you could just copy  the selection to a new worksheet.
You may need to select the entire column in your case though.