Precision 450 Processor

Would anyone know what the exact processor spec is on a 2.8GHz Dell Precision with a 533MHz FSB? I am trying to get a second processor for it but don't know its core stepping, and hence can't tell which of SL6YQ, SL6VN, SL6GG, SL72F, SL73N or SL6NS I need to go for? :-)

PS: If it helps, I've bought the Dell in the UK.