I'll put an theoric example: In the same MDD 1.5 Gb RAM :
All Instruments are 100 Mb each:
Logic plus EXS:
7 instruments with 200 notes of polyphony.
Cubase plus Kontakt:
14 instruments with 100 notes of polyphony.
Cubase plus Halion:
24 instruments with 200 notes of polyphony.
This is why Halion is the winner. And the second is Kompakt. And about EXS, 200 notes of polyphony are useless with just 7 instruments.
You make me want to try Logic + Halion...

There is also Cubase + EXSP24... Maybe using the 1 Gig Ram trick from DieHard and limiting memory in other way you could use without the freezes/hangs off the system.