Actually, the Future Tech rollover occurs at FT 167; and again 255 is the magic number for the rollover (88 regular techs + 167 Future Techs). Once FT 167 is reached (at a cost of 32,000 beakers), the cost per tech resets to the starting level of 10 beakers for FT 168. Hence, one can usually go from FT 168 to FT 255 in as a little as five turns.