Both events may find success brings its own pressures as Download chief John Probyn saw his festival enjoy a record-breaking year with daily crowds averaging well more than 90,000 fans. Meanwhile, Stuart Galbraith and John Jackson will be keen to make sure the global – or at least pan-European – expansion of Sonisphere doesn’t stall in 2011.

At the recent Virtual Festivals conference, Galbraith admitted that growing Sonisphere carries the risk of the occasional disaster where the crowd sizes are lower than expected, but “tweaking” the business model should ensure there are enough successful ones to more than counterbalance the loss-makers.

The real trick is to eliminate the loss-makers, or at least the countries where people may be keener to riot in the streets to protest government cuts than buy a festival ticket. But maybe that’s over-simplifying the issue.

In the last two weeks, the UK has had student riots that have hogged the front pages of the national papers, but it’s doubtful Galbraith and Jackson ever considered scrapping its English Sonisphere at Knebworth Park July 8-10. Slipknot and Biffy Clyro are its first two headliners.

The UK Sonisphere hasn’t matched Download’s pulling power, although The Guardian says it’s still Britain’s “premier metal festival.” The Live Nation gathering had a five-year start and competing with it is a local issue compared to establishing Sonisphere as a global brand. The UK bill will also have Metallica, Slayer, Megadeth and Anthrax.

Download has just announced Linkin Park and System of a Down will each headline one of the three nights, but the festival’s regular fans have become confident of the festival producing value all the way down the bill. It will always be a difficult event to out-sell.

Galbraith may have the personal challenge of beating Download, which he helped start in his time at Live Nation, but in the shorter term he’ll likely settle for the support of papers like The Guardian and Kilimanjaro Live – his joint-venture with AEG – winning one of the recent Digital Entrepreneur Awards.

Download focused on electronically communicating with its fan base, so Galbraith and Steve Jenner – the Virtual Festivals founder who’s also Kilimanjaro’s digital director – would have been particularly pleased to collect the Dead Cert Award.

It recognised the company’s exceptional commitment to online performance in marketing and commerce across its portfolio of events.

Apart from announcing the Knebworth dates, headliners, and putting the show on sale Dec. 10, Galbraith and Jackson – who owns London’s K2 agency – haven’t confirmed where the mainland European Sonispheres will be held.

Galbraith told Pollstar there will be “between 12 and 14 of them,” although the final details won’t be revealed until after the “tweaking” he explained at the VF conference.

The day the Knebworth tickets went on sale, Galbraith was in Switzerland to look at a new site with local Sonisphere promoter Harry Sprenger of Free & Virgin. Last year’s gathering pulled more than 55,000 and it will be surprising if there isn’t another Swiss Sonisphere in 2011.

Two new Sonispheres in the offing will likely be a French version promoted by Salomon Hazot, who recently sold his Nous Productions to Warner France but hung on to his festival business, and an Italian edition likely promoted by rock specialist Andrea Pieroni, who recently sold the major part of his Florence-based Live In Italy to Live Nation Italy.

There are no obvious casualties from the 2010 Sonisphere roll call, as a disappointing crowd in Czech Republic was at least partly down to a late change of site due to difficulties with a local mayor.

Ewald Tatar from Austrian promoter Nova Music has already indicated that his company is keen to do a second Sonisphere in 2011.

The four Balkan Sonispheres in Bulgaria, Greece, Romania and Turkey may have attracted 310,000 people at an average of more than 34,000 per day, but it’s far from being Europe’s most affluent region and the current financial indicators suggest Galbraith and Jackson may struggle to equal those numbers in 2011.

Already tweaked out is the Dutch Sonisphere, where the festival’s 2009 debut didn’t half-fill Nijmegan’s 70,000-capacity Goffert Park, but the failures have been balanced by some spectacular successes.

At the end of June, Galbraith reported the first Polish edition pulled nearly 100,000 to a private airfield in Warsaw’s Bemowo district. Steve Todd from Live Nation’s Warsaw office – which co-promoted the event – said “it was the best-selling outdoor shows that we’ve ever promoted.”