Best-ever Aussie pace attack?

Test legend Glenn McGrath has declared the current Ashes arsenal equal to the best Australian fast-bowling attack he's ever seen.

On the back of Australia's domination of England this summer, McGrath has boldly rated the current pace trio ahead of any of the great attacks led by all-time champions Dennis Lillee, Jeff Thomson and himself.

"Looking at the way the bowling unit has gone about its business this series, it's been as good as I have ever seen," McGrath said.

Spearheaded by Mitchell Johnson's stunning resurrection, Australia's quicks have taken 58 wickets at a formidable 19.77 to set up a potential 5-0 whitewash at the SCG starting on Friday.

Three-time man of the match Johnson has 31 scalps at 14.32 and has taken a wicket on average every 32 deliveries during the four Tests.

A big performance to finish off in Sydney will put him in elite company as one of the highest wicket-takers ever in an Ashes series.

Ryan Harris has taken 14 wickets at 26 and looks set to brush aside a knee injury to see out the series, while Peter Siddle will have a chance to improve on his record of 13 scalps, also at 26.

Lillee is considered Australia's greatest fast bowler and terrorised batsmen alongside Thomson in the 1970s and 80s.

McGrath, with 563 Test wickets at 21.64, led a fearsome era of fast bowling across two decades featuring Jason Gillespie, Craig McDermott, Michael Kasprowicz and Brett Lee.

But McGrath is confident even the "Fast Bowling Cartel" would have Johnson, Harris and Siddle at the top of the tree.

"I think the FBC would all probably agree," he said. "They have got good bowling plans, they are bowling well, they are executing their plans well and it's working. There's no weak link in the unit."

There are concerns over the fitness of Harris and Siddle at the end of a long campaign, but Australia are expected to become just the fourth side in history to stick with an unchanged XI for the duration of a five-Test series.

Looking ahead to next month's tour of South Africa, bowling coach McDermott's fast-bowling squad will likely be backed up by the outstanding James Pattinson, who has recovered from a back injury.

However, it's Johnson who has emerged as the key man for Australia. The left-armer only needs four wickets to surpass Geoff Lawson as the highest wicket-taking Australian fast bowler in a five-Test series.

If he takes nine he will become one of only six players to have claimed 40 wickets or more in an Ashes campaign.

McGrath described Johnson as the most intimidating bowler he's witnessed.

"It's all about attitude and aggression. You need someone to lead the attack and he is well and truly doing it," he said.

"I can't remember the last time someone has bowled with such hostility and had such an impact ... he's not only taking wickets but lifting the team as a whole."