Count the unique items in column F if E:E = "Chris" and M:M = "VIC" and N:N = "PT"

How "massive" is "massive" ?

These types of calcs are generally quite expensive - if you try to run them over entire columns (not possible pre XL2007 for good reason) you will notice some severe lag / crash

There are generally speaking a couple of approaches - ie a SUMPRODUCT approach and also a Frequency Array

The Frequency Array might make more sense here

=SUM(IF(FREQUENCY(IF(($E$1:$E$1000="Chris")*($M$1:$M$1000="Vic")*($N$1:$N$1000="PT"),MATCH($F$1:$F$1000,$F$1:$F$1000,0)),ROW($F$1:$F$1000)-ROW($F$1)+1)>0,1))
confirmed with CTRL + SHIFT + ENTER
(Enter alone will not suffice)

For sake of demo note shortened range references, adjust as you see fit.

(you might want to consider using dynamic named ranges - prob. created with INDEX rather than OFFSET to avoid Volatility)