IIRC, not even TI will support running the 3430 series chips past 600MHz, and they even specify a maximum safe runtime at 600MHz. Fortunately, TI's process is decently tolerant of higher clocks and you probably won't hit any issues so long as you don't spend too much time clocked up beyond 600MHz. I'd wait for the 36xx chips (or just a litho shrink in general) before going for higher clocks anyway, simply due to the gain in power efficiency and, thus, thermal efficiencies.