I do not have an answer to your direct question. However there is much room for improvement in a new 17" MBP. They could have dual mass storage available (any combo of SSD and large HDs), more available RAM, latest GPU, new displays, evolutionary pricing, etc.
The landscape of the 17" MBP world may change at Mac Expo SF in January, which would likely include lower prices for existing 17" MBPs. IMO Mac Expo SF and/or OS 10.6 (expected June at WWDC, maybe sooner) is the earliest that anyone with a currently good working system should consider upgrading.
-Allen Wicks