As andyc has pointed out, you coudn't get away with Symonds as your fifth bowler at this level of cricket. Australia were always pushing it a little bit when they did it even in regular ODIs which is why they were so keen on developing Watson into a one day player in the first place (he was really unnatural in the format in general at the start of his domestic career, somewhat ironically). At a level above against other nations' ATG sides Symonds would really be exposed. Awesome sixth bowler to fill in a few of someone else's overs when they're having a bad day, especially since he could bowl both pace and spin, but that's the extent of his bowling.
The way I see it, in terms of the top seven; Ponting, Bevan, Hussey, Gilchrist, Symonds and Watson must all be there. I'm not too fussed where Watson bats but he has to play, so if you want to play Hayden or open with Mark Waugh then it means Bevan bats four. Like andyc though, I'd be looking at:
1 Gilchrist
2 Watson
3 Ponting
4 -
5 Symonds
6 Bevan
7 Hussey
8 Warne
9 Lee
10 -
11 McGrath
I think I'd lean towards Lillee and Greg Chappell for the two spots left, but I'm not all that fussed really - could just as easily be Jones, Waugh, Martyn, Hayden with a reshuffle, Bracken, McDermott etc.