In that shallow even the full bore 1Kw is over kill ...you could get a 256 with wider cone angles and be better off...than the narrow cone angle of the 260's !!
1 kW is more than enough. Not sure I agree with the wider beam, however. I prefer the narrow beam for better target discrimination. Similar to comparing the picture of an open array radar to a dome (with the open array providing a better target discrimination in most cases). If it's a dual frequency unit, you can switch to the 50 kHz mode which would be the wider cone angle.