The two great sounding Kuassa Rack Extensions Vermilion and Creme (guitar amp simulators) are updated today for additional oversampling options. Oversampling techniques were added to prevent aliasing. This can become a problem when you saturate a signal that will create overtones which, when they are higher than half of the sampling rate (in case of 44.1: above 20 kHz), are nasty and non harmonic.
I have tested both Rack Extensions and the 8 times oversampling setting is really smooth. Choose a lower setting if CPU usage is an issue (you might leave it at its default setting and only change it when mixing or making a bounce).
P.S. It seems that these oversampling options are only available for the RE versions of these lovely virtual amps. Great news, guitar players using Reason have all the luck!