Well it would run fine on either one. But if its some other thing like gaming is your option as well, i suggest i7 730.
Speech recognition softwares are not that demanding on the PC. If you want it only for the above two mentioned reasons. X6 1055T would do just as good. But in that price bracket i5 750 would also be a good choice.
Dragon Naturally Speaking isn't a multi-threaded program. But it can share it's workload across multiple CPU cores.
For DNS CPU still speed matters more than the number of cores. As hell_storm2004 says DNS isn't that that demanding a software program. DNS spends most of it's time waiting on input from the user.
Have you thought about your overall budget? You can get a good CPU to match what you want to spend.
i7 870 2.93Ghz (turbo boost 3.6Ghz) @ $290 would be a better CPU choice than the i7 930 2.8Ghz (turbo boost 3.06) $290
X4 965 3.4Ghz @ $197 would be a better CPU choice than the X6 1055T 2.8Ghz (turbo core 3.3Ghz) CPU @ $200.
i5 760 2.8Ghz (turbo boost 3.3Ghz) @ $210 is a good value and should be 'as good' as the X4 965 and X6 1055T.
AMD Turbo Core - x6 1055T can run 3 cores @ 3.3Ghz while 3 cores are sent to 'idle' @ 800Mhz
Intel Turbo Boost - Core i7 870 2.8Ghz stock, 4 cores turbo @ 3.2Ghz, 2 cores @ 3.46Ghz and 1 core @ 3.6Ghz.
-> Even the better dual core CPUs have plenty of power to run DNS and support an excellent movie and multimedia experience.
i5-661 3.3Ghz (turbo boost 1 core @ 3.6Ghz) @ $210 (has a video chip on the CPU - doesn't require an additional video card)
Phenom II X2 555 Black Edition Callisto 3.2GHz $100