I'm using only one SMP2 client on my quad core. This also allows for a huge bonus. If I decided to fold with my GPU I would lose more points with the CPU client than I would gain with my GPU. This is mainly due to the fact that the quicker you complete a work unit the larger the bonus.
The work unit (project 6023) that I am on now gives 475 base points.
Base points are the points given for completing a work unit before Final Deadline
Completing a work unit before the Preferred Deadline gives a bonus (That is after completing 10
FahCore_A3 WU's with a
Passkey).
My bonus is 2530 points.
My total is 3005 points every 7.5 hours.
It's the SMP2 bonus that makes my points so high and would reduce tremendously, if I was to donate a core for folding with an ATI GPU client.
I find this large bonus to be discouraging to those that are not capable of running the SMP2 clients. I find the bonus points to be unfair when compared to those who don't get them.

I can only hope that one day those that have been discouraged will one day rejoin the folding@home project.
If I wasn't using a SMP2 client, I would need one client per core. Even with the SMP2 client a "-smp" switch must be used for the client to use all cores. Without this switch the SMP2 client will work as a normal client and only fold on one core.
The "-smp" switch or any other switch can be added during setup when the "Additional Parameters" question is asked. You also have the option to add the parameters within the shortcut properties.