Is it worth the investment? It depends. The Intel "recommended" price for any of them is about $1100 USD. The Xeon E5-2650 has 8 cores and 16 threads (with hyperthreading enabled). There are 2 models. One is a 2Ghz chip with a turbo speed of 2.8Ghz, and a 2.6Ghz model with a 3.4Ghz turbo speed.
What do you mean by "multiplier locked"? Do you refer to the system clock speed? CPU speed? What?
My work laptop has a 2 core i7. My personal home workstation (now 6 years old) has dual quad-core E5450 3GHz Penryn processors - out of date now, but still quick enough for my needs. Would I consider the investment? Definitely if I were building a new workstation for my personal use. You also need a motherboard to complement that chip.