Our recent analysis of the 100 most expensive motorcycles ever to have sold at auction left no doubt as to the most sought-after marques by elite collectors. Brough Superior is the most prominent marque in the top 100 with 23 motorcycles, and Vincent is second with 14 motorcycles.

As the list expands to the top 200 over time, we expect the most popular marque will become hotly contested between the two brands as more than twice as many Vincents were made (approx. 6872) than Brough Superiors (approx 3000) and between three and four times as many have survived – hence when the list expands to the top 200 then 300, there will be more Vincents to populate it.

Now two pristine examples of the world's most sought-after motorcycles are to cross the auction block on the same day – November 30, 2014 – at Bonhams' London headquarters in Bond Street. Both look certain to move into the top 100 most expensive motorcycles of all time, and the 1929 Brough Superior SS100 Alpine Grand Sports is such a perfect example of the breed that it will most likely become one of the top 10.

Estimated by Bonhams to fetch between £270,000 (US$435,240) and £320,000 (US$515,840), such a price would put the 1929 Brough Superior SS100 Alpine Grand Sports somewhere between the 1915 Cyclone Board Track Racer, which sold for US$551,200 in July, 2008 and the George Brough's personal 1939 Brough Superior SS100, which sold for £253,500 (US$425,943) earlier this year at Bonhams' Staffordshire sale. Those bikes currently hold third place and ninth place on the all-time list.

In 1929, the average wage in Great Britain was £3 per week, so the Alpine Grand Sports cost roughly sixty weeks wages

The 986cc SS100 Alpine Grand Sports model is named after the famous Alpine Trial, one of the very first alpine reliability trials and prior to WWI, the toughest event in the world. Beginning in 1910, the Alpine Trial took in the vast mountain peaks, chilling temperatures, and the twists and turns of Austria, Croatia, Slovenia and the infamous Stelvio Pass. It evolved into what is now the World Rally Championship, though initially, it saw both cars and motorcycles compete.

George Brough participated in the Trial in 1925 on an SS100, winning six trophies including one for "Best Performance." The design of the Brough Superior Alpine Grand Sports took inspiration from its founder's achievement, and was introduced to the market in 1925 for the 1926 season with a lower compression ratio (making it suitable for touring), a small fly-screen and a pair of tool boxes as standard.

"Brough Superior is a legendary marque in the motorcycle world," said Ben Walker, Director for Bonhams Motorcycle Department. "The most charismatic of the marque's stable is unquestionably the SS100 and we are delighted to be offering the model in its ultimate guise, a Vintage example in Alpine Grand Sports specification, boasting matching registration, frame and engine numbers – designed to honor the legendary Alpine Trial – the most arduous motoring test of its time."

The 1950 Vincent which will go to auction on the same day was the fastest motorcycle of its day, with a top speed of 125 mph. Though Vincent currently has 14 motorcycles in the top 100 compared to Brough Superior's 23, a further ten Vincents occupy the most expensive list between positions 101-120.

The 998cc Series C Black Shadow has matching registration, frame and engine numbers, and Bonhams' estimates it will fetch between £70,000 (US$112,840) and £90,000 (US$145,080), which means it might also get a spot in the all-time list if it sells towards the top of the estimated price range.

The duo will be on display at Bonhams London to Brighton Run sale preview held at 101 New Bond Street this week (October 30 - 31), and will also take part in the National Motorcycle Museum's 30th Anniversary celebrations this Saturday, November 1.

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