This trend it leaves perplexed to me.

A simple, very simple code:

SET ESCAPE ON
* BURN IN
FOR k=1 TO 2000000
NEXT
t1=SECONDS()
FOR k=1 TO 20000000
NEXT
T2=SECONDS()-T1
t1=SECONDS()
FOR k=1 TO 20000000
 =.T.
NEXT
T3 = SECONDS()-T1
? T2, T3 - T2
* vfp6.5 : 1.212  1.073
* vfp7.1 : 1.175  0.824
* vfp8.1 : 1.040  1.616
* VFP9.b : 1.136  2.716

I aspected near values with this simple code.