used my SCS PactorIII modem (first installed in 2000 and upgraded twice since then) and an ICOM 710RT during our Seattle to San Diego trip in September (you can read all about it at www.svmirador.net - especaially how the grib files kept us from sailing into a 45 knot / 20 foot seas weather situation).

I downloaded GRIB files every six hours. I would typically request COAMPS model data on a 0.2 degree size - that produces a unique wind estimate for each 14 mile square of water. I would request that for the next 48 hours which is about 300 mile in Mirador's case (5 degrees) and generates a compressed file to send of about 4K bytes. I would also request a 4 day GFS model file that would provide wind estimates for much larger areas over a 12 hour interval - those were also about 3k to 5K to receive.

I receive data at 3.5K to 5K characters per minute so a typical high density so it would usually only take one to two minutes to get each GRIB file.

I have been using GRIB data and the Pactor/ICOM since 2003 and have always been very happy with it.