Hi I am a first time builder and I am looking to build, after port, driver & brace loss, a 12.6 ft 3 LLT tuned to 15hz. After running what I think is the right numbers in WinIsd I end up with a port velocity around 47m/s. Is that a high number or an accepted number. I am going to run it off an EP-2500 and put in a number of 850 watts. One last thing is it better to use the SDX 15 or move up to an IXL 18.4. Not too much to pick from here in Canada.Thanks in advance!!!