Re. the FFT-length issue: Since it wouldn't help anyone else "steal" credit for your work, could you (the original poster) give us at least the next 2 digits of the exponent? According to my calculations, the upper limit for safe testing at 1792K is around 34.5-34.6 million using SSE2 floating arithmetic, slightly higher if using an older x86 without SSE2 support (i.e. 64-mantissa-bit register floats).