cjl :
Although, if the OP can wait, Intel will be coming out with the Nehalem 4p and 8p setups, which can have up to 8 cores per CPU and 8 CPUs and 2 threads per core for up to 128 threads in a single server.
Here's what's coming up by early 2010:
1. The "Beckton" Xeons you referred to, which are 8-core, 16-thread CPUs used in machines with 4-32 sockets. These are 45 nm chips with 8 cores and 24 MB L3 cache all on one huge die, so they will be
very expensive. I'd say at least $3000 each since the "only" six-core 45 nm "Dunnington" Xeons with 16 MB L3 cache start at $2000, and the Becktons are going to be even bigger with lower yields.
2. AMD's 12-core, 12-thread "Magny-Cours" Socket G34 Opteron CPUs, which are an MCM comprised of two six-core CPUs with 6 MB L3 cache. These are available in two and four-CPU setups, so you could get 48 cores/threads in a four-socket machine. These will probably be a bit less expensive than the Beckton Xeons because of the smaller dies used to make the CPUs.
3. Intel upgrading its current stable of 45 nm quad-core Nehalem-based Xeon DPs to six-core 32 nm units. These will give you 12 cores/24 threads in a two-socket box, which is nice but probably a bit small for the OP's needs.
4. AMD refreshing its Socket F platform and then migrating the single- and two-socket Opterons to the new Socket C32. C32 is basically Socket F with DDR3 and can support one or two quad- or six-core CPUs. This is also going to be a bit small for the OP.
In short, it depends on exactly how much power the OP would want. A quad 12-core Magny-Cours Opteron setup will be most likely be considerably less expensive than a quad Becton Xeon MP and have a 50% core count advantage, although the Opterons will top out at only four CPUs and 48 cores. If he needs as much power as he can get, he'd have to go with the Xeon MPs since they can be run in an up to 32-socket configuration.