SO what's the big thing the Championship has taught us this year?

That the French were caught sans culottes when it got a bit parky in Paris? That an Irish side who have lived by the last-minute kick were bound to die by one eventually? That England are on course to become the worst team – worse even than the Wales of 2005 – to win a Grand Slam? That a dollop of luck and a bit of self-belief could turn Italy into a genuine force?

All of the above. But amidst the agonies of Scotland and Ireland, the ecstasy of Wales and the bewilderment of England, there ought to be a leavening dose of realism borne of the fact that all of the games have been compellingly close spectacles. Only two of the five matches have been won by margins that would not have been wiped out by a converted try, and no side has gone through an entire game sitting firmly in the driving seat.

Except, you might argue, that Scotland did in their opening match against England – and we all know what happened there. Scotland walloped England for possession and territory, taking 60% of the former and 58% of the latter, remarkable figures for a beaten side in an age when those numbers would normally produce victory by a street. The last side to lose after such a dominant performance was, ahem, Scotland – who somehow managed to lose 37-17 to Italy in 2007 after virtually wiping them off the park.

But let's get our noses out of our own midden for the moment. Let's look instead at England – and, specifically, at their clash with Wales at Twickenham on Saturday, a game that already has the look of the championship's defining contest. Perhaps not the deciding contest, as both will still have to play France, but it will answer a lot of questions about how good or how bad the respective teams are.

It should also say a lot about Stuart Lancaster's prospects of turning his role as England caretaker coach into a permanent arrangement. It has comforted England's detractors to say that Lancaster has simply enjoyed the beginner's luck (and the eagerness of players to impress) that so often comes the way of a new coach, but a new assessment will be needed if his side can beat Wales.

What Lancaster has unquestionably instilled is a discipline and work ethic that England had jettisoned long before the embarrassing shenanigans of last year's World Cup. The yeoman values have returned, most conspicuously in defence. To slaughter Scotland for poor finishing against Lancaster's lot is to miss half the point, for England also turned in one of the greatest defensive performances the championship has seen.

For that, they relied hugely on their tactic of committing as few bodies as possible to the breakdown. "You play, we'll tackle," they said to Scotland, and it worked. Hence the silly numbers at the finish – the silliest of all being the 13-7 scoreline in England's favour. But it did the job of giving Lancaster the winning start without creating one iota of over-confidence among his players.

They rather scraped it in Rome last weekend as well. But can they really go through an entire tournament this way? All scrape and no swagger? Most pertinently, can they douse the dragons of Wales without breathing a little fire of their own?

It is the toughest call of Lancaster's brief Test career. He has dynamism on tap in the shape of the fit-again Toby Flood and Courtney Lawes, but would he dare to drop Charlie Hodgson, the man whose charge-downs have delivered two tries? Bringing Lee Dickson in for the unimpressive Ben Youngs at scrum-half is perhaps an easier call, but there must also be a loud voice at the back of Lancaster's mind telling him not to change the winning formula.

And then, of course, there's Wales. They haven't exactly made a habit of winning at Twickenham in recent years, claiming just one victory from their last 13 visits to the Cabbage Patch, but another triumph this year would give substance to the argument, no more than a whisper in the Valleys just yet, that they are pulling together a team who will someday be mentioned in the same reverential tones as the great side of the Seventies.

In Scotland, we will have the luxury of the armchair view on Saturday afternoon. After which, we can start worrying about our own lot.