The Davis Vantage series does indeed update every 2.5 seconds. If they did it any more frequently, it would be too big a power demand for the little solar cell.

The TackTick instruments only have to broadcast 10-20 meters. The Davis instruments can easily go 100 meters and, sometimes, much more. I have one that goes 100 meters, plus through 3 exterior walls.

Weather at our house: http://threefools.org/weewx/

Weewx (the open source software on which it's based): http://www.weewx.com

-tk