'Roughly speaking'

On my Mercian travels, I revisited Lincoln Cathedral to marvel anew at its sheer scale and breathtaking beauty. This, in my humble opinion, is the greatest building in England. And so it was in the rather less humble opinion of John Ruskin, who declared that 'I have always held and proposed against all comers to maintain that the Cathedral of Lincoln is out and out the most precious piece of architecture in the British Isles and roughly speaking worth any two other cathedrals we have.' 
I love that 'roughly speaking', as if Lincoln might be worth only one and three quarters other cathedrals, or perhaps two and a quarter – far be it from Ruskin to lay down the law.