When we were on a single server, with ~20 agents on it, loadavg was around 1.4-1.5 with rare spikes to around 2.5-2.8 with predictive dialing with max ratio 5.
Dell 1850, 2 x 3.0GHz Xeon HT, 2GB RAM, 2 x 36GB SCSI disks in software RAID1, Debian 4, 64 bits.
Here is the old info I've posted before we moved DB and apache to another machine:
http://www.vicidial.org/VICIDIALforum/v ... 3454#23454
However, since you do not have problems, don't worry too much