I did the walk up to the top of Flinders Peak in the You Yangs - according to Parks Victoria at http://www.parkweb.vic.gov.au/1park_display.cfm?park=208, this is the highest peak in the You Yangs. Elevation is officially 340m, but my GPSr read 345m at the base of the steps up to the lookout platform where I recorded the coords. Lots of steps (in fact there are apparently 450 of them), but otherwise the walk is not too tough - just over 1.5km from the carpark with a 200m elevation change once you are standing on the lookout platform (pictured).