David Leggat: Steve Smith's star turn a challenge for his rivals

Steve Smith of Australia during the 2017/18 Ashes Series. Photo / Getty Images

They have been been regarded as test cricket's Big Four in the past couple of years. Steve Smith, Virat Kohli, Kane Williamson and Joe Root, all captains of their country and the four best batsmen in the game.

But has the fidgety Australian Smith eased himself clear to the point where there is a gap between him and the other three?

Smith's second test double century to bury England's bowlers at the Waca moved him, at least for the moment, to second place behind only the legendary Don Bradman among the greatest test batsman on averages, and certainly among Australians.

He was out early yesterday at 239, his second test double ton and eighth hundred since the start of last year. Considering this is his 59th test, and it took him his 12th test to register his first, he's fair rattling along.

Kohli has bagged six double centuries among his 20 hundreds and got three in his past three tests against Sri Lanka. His average has leapt after the two double tons at Nagpur and Delhi in the past few weeks.

Root is having his battles trying to hold England together in Australia.

Williamson's past six test innings, spread over two seasons, have made 2, 1, 176, 1, 43 and 54, a mixed bag.

New Zealand's shortage of test opportunities hurts Williamson and until the newly rejigged test timetable is revealed, possibly in February, the picture for the immediate future won't become any clearer.

Williamson is confident New Zealand will have more test opportunities coming, as is New Zealand Cricket's chief executive, David White. Leaks out of the International Cricket Council - erroneously White has insisted - painting a bleak test future for New Zealand, haven't helped.

Back to Smith, whose 22nd test hundred in Perth came in his 59th test. Only Bradman, in 38 tests, has done it quicker for Australia.

It is Smith's 14th century as captain in his 29th test in charge. It took Bradman 24 tests to that mark.

One point about the Waca, without decrying Smith's achievement, is that in it is a road for batsmen. Six batsmen made hundreds there two years ago, including Ross Taylor's 290 and Williamson's 166 - and Smith.

The search for the "next" Bradman has haunted decades of Australian rising stars. None, statistically, could, or could be expected, to live up to the Don, who was so much more than a run machine in Depression-era Australia, a figure of inspiration and hope in desperate times for a start.

Comparisons between the four? Kohli is, at 29, the oldest; Root, who turns 27 on December 30, the youngest.

All damage bowling attacks in different ways. Expect the other three to view Smith's progress as a challenge.