Hyperthreading boosts or slows down Domino? (SLES8, Domino 6.5.1)

Dear all,

i am running Domino in a cluster on two HP ML 570 with 2x Xeon 2,8 Ghz. (2
MB L3)
Hyperthreading (HT) is activated so Linus shows 4 Processors.....
Affect is that Availability Index is jumping from 0 - 100 sometimes even
there is less workload. Ok i now that internal calculation of Avail.Index
in R6 has changed and this behaviour is quite normal...

But basically i would like to know, if Domino can scale 2 virt. cpu's or
not. ?
I am feeling that Domino will get more data throughput with HT
deacitivated, using only two strong physical cpu's. Further i red that HT
is slowing down linux generaly with Kernel .20 or .21....

Anybody got already some experiences with this issue or already done some
workload comparisons with HT on/off.
Any help/hints are highly welcome.

thanks and best regards,
Alex