''Australia have the best attack inn [sic] the world #Ashes2013,'' tweeted fast bowling coach Craig McDermott on Monday morning.

Peter Siddle, the most unsung member of the trio that has dismantled England in this Ashes series, did not back away from this assessment, which the Australian pace posse will undoubtedly try to prove when they tour South Africa in February and March.

''We're up there, aren't we?'' said Siddle, who declared the quicks were thriving because they no longer feared for their positions in the side, because they were experienced and disciplined enough to bowl maidens upon maidens until England cracked, and because the batsmen have given them big leads to bowl to (setting England 500 or more in the fourth innings in all three Tests).

''This is definitely the best line-up I've ever played in,'' Siddle said.

McDermott wasn't just talking about the starting quicks - Siddle, Ryan Harris and Mitchell Johnson, versus Steyn, Morne Morkel and Vernon Philander.

He believes Australia has superior depth, an assertion that will be put to the test if Harris or another of the quicks can't recover for the Melbourne or Sydney Tests.

The Proteas could also have to explore what lies beneath their champion pacemen. Morkel sprained an ankle during the epic drawn Test against India at Wanderers, prompting the selectors to bring Kyle Abbott, part of the next wave of South African pacemen, who has played just one Test, into the squad as cover.

''It's not just the bowling attack that's on the field. I think it's the back-up we've got as well,'' McDermott said later. ''That'll maybe be put to the test over the next couple of weeks. We'll see.

''I didn't tweet that for any other reason. I think we've got the best attack in the world. It's very well balanced, particularly with Nathan [Lyon] as our spinner - he's bowled well - and you've got 'Watto' [Shane Watson] there as your fifth bowler.''

The faces in the Australian attack are not much different from the 2010-11 Ashes. But a lot has changed, not least Johnson's radar.

''We're in a good place at the moment. We've been striving for a long time as a bowling unit to get that consistency right, and to get the complete innings together,'' Siddle said. ''This series has shown that. We've been able to bowl teams out quite quickly, give our batters a big chance and put a lot of pressure on the opposition.

''We always speak about building pressure, but also consistency. Over the years we haven't been able to build partnerships from either end.

''And it's always nice when the side isn't changing - that gives the boys a lot of confidence. When you're playing well and winning Test matches, the side doesn't change. Blokes are not worried about getting the axe or worrying about that next game, getting that five-wicket haul or that hundred runs. Every contribution counts, and that's what is happening in that side at the moment.''

There is some doubt about Harris' fitness because of his sore knee, as there was before the third Test at the WACA Ground, but he bowled at training on Monday and will do so again on Christmas Eve.

Australia's formidable depth was on display in the MCG nets, where Doug Bollinger, James Pattinson and Jackson Bird joined in the Australian session. Siddle is confident Harris will play on Boxing Day.

''Ryan Harris looked like that [proppy] before the first Test. He's always going to look like that. He's 34, obviously he's battled a lot of injuries, but he pushes through. It's a positive when he's like that.''