The PS3 version of the original Rainbow Six Vegas game didn't run as well or look as good as the Xbox 360 version. However, the PS3 version of Rainbow Six Vegas 2 will not be a port of the Xbox 360 version, its developer has said, but admitted that there will be "slight differences" between the two versions, including lighting.
Gamefront.de has posted the UBISOFT PAL territory release schedule listing this game for both X and PS3 for Q1 2008 (I believe this would be fiscal Q1 which would mean Apr-Jun AFAIK).
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I think this news "didn't run as well or look as good" might negative impact (decrease) PS3 version sales.