Don't look at time to first error. Use memtest and look at total number of errors after 100% test. Again, some chips are just not designed to work at high frequency.
Please check if your sticks are single sided? If YES then you most probably have infineon chips (ce ones?) - they don't like high voltage, don't go over 215-230 Mhz even with relaxed timings but can do nice CL2 3-2-7 @ app.215Mhz. then you need to lower your RAM clocks but with better timings.