I've tried the following test:

lnTime1 = SECONDS()
SELECT style FROM Styles WHERE Styles.Style NOT IN ("F","S","X","D","M", "CD", "PK") AND NOT Style like '%.%' INTO CURSOR curT
lnTime2 = SECONDS()
SELECT style FROM Styles WHERE NOT INLIST(Styles.Style, "CD","PK","F","S","X","D","M") AND NOT Style like '%.%' INTO CURSOR curB
lnTime3 = SECONDS()
lcStr = "IN Clause " + TRANSFORM(m.lnTime2 - m.lnTime1) + " sec. INLIST Clause " + ;
           TRANSFORM(m.lnTime3 - m.lnTime2) + " sec."
=MESSAGEBOX(m.lcStr)
_cliptext =  m.lcStr 

and both selects gave me 18 sec. I open Styles with Index Styles (on Style) before running these select statement.