Though L5420 is a pretty fast processor and when used in a configuration of 2, it should give you a top-end performance provided the other components of your computer are in compliance however since you can wait for another 3 to 5 months and I am assuming that you won't be having any budgeting issues (as you're already getting 2 x L5420), and you have asked if there is something on Intel's roadmap till then, I have some interesting news for you coming up this September.
Intel's Nehalem based 45nm, Quad-core, octa-threaded microprocessor "BLOOMFIELD"
Read the references for yourself and I am sure you will be glad to know that you are looking into something even better than what you have at the moment, future!
However you must keep this in mind that L5420 is a Xeon while the Bloomfield is going to be released as a desktop processor which if customized well, a powerful desktop should be able to do graphic rendering for you giving you an impressive result. I am discussing Bloomfield here since you asked if there was something new Intel was coming up which will bring in revolution to the chip based computing, you were concerned about more cores and even lesser power usage ... let me present you future, Bloomfield!
In case you are a bit sceptic about something, feel free to ask, it's here for you to see and choose.