+10000 to Sennheiser.
We use 172's here. One has served me for over a year on a weekly basis(in the RF-filled Houston area, using C band) and now my 17 year old has one for use in his High School Marching Band(he marches with a white Steinberger). I DID call Sennheiser to confirm with their techfolks that it would cover a football field. Sure does!
IF you get one, make SURE you contact their tech folks and look at this chart
http://www.sennheiserusa.com/newsite...qfinder-ew.asp
for the frequency band you'll want(there was A, B, & C for the 172) depending on where you perform.
Some of the "dealers" are not too sharp on this but Sennheiser codes the Band into the numbering on the boxes.
You may want to look at the chart and consider this one(NOT mine):
Sennheiser Wireless EW172-G2