Tango,
I have the PLV-Z5 and I am using a 35ft hdmi (22ga) from monoprice. NO problems whatsoever!!!
Great picure and no "sparklies".
I am using it in a totally light-controlled room with a throw of ~12ft and using a screen size of appx 100". Seating is at appx 11.5ft.
I have no problems but 18 ft is a longer throw and MAY require higher contrast performance.
Check the comparison Review:
http://www.projectorcentral.com/ax100u_plv-z5.htm
It has some good info abouut the capabilities of the Sanyo. I ended up going with the Sanyo based on the honest assessment of it's capabilities and my application.
HTH