I’m sure intel’s new xeon chip will come out by the end of the year, in small quantities and specifically for apple first if we consider apple’s history. It probably won’t be until February or even March until other companies can ramp up production in large quantities for dual-socket systems. I can’t say whether it’ll be worth waiting 7-8 months for, but I don’t think buying a current system would be necessarily bad either.
Bear in mind that even though the the new xeon’s cores are increasing from 8 to 12, there’s a highly likely chance the clock speed per core in multithreading will be lower to compensate for the additional wattage/heat from the added cores. That’s always how it’s been.
The new xeon’s turbo mode will probably boost single-threaded performance by around 9-14%. I think total multithreaded performance will likely increase around 30% real-world and 40% max under certain conditions, but not the 50+% a lot of people might automatically assume going from 8 to 12 cores and to a slightly more advanced architecture. Going from 32 to 22 nm isn’t enough of a jump in thermal and wattage capability to get a 50+% performance gain. Since core count is increasing 50% (which is a lot), clock speed will have to lower to compensate to meet their wattage/thermal constraints for the chips. Going from sandy-bridge to ivy-bridge is a minor performance bump compared to the last xeon’s architecture upgrade going from westmere to sandy-bridge.
Dell and HP’s build quality might not be as good as some, but their systems come with extensive warranties (or can optionally extend) and provide reasonable capabilities. If someone is concerned enough about build quality for a workstation when they open up the machine to add in parts or doing maintenance, they probably should either hand-build their own system since they already have that knowledge of knowing exactly what they want, or pay even more for a more expensive vendor to custom built something that isn’t mass produced on a huge scale.