All strikers struggle, regardless of whether they are British or not. Other than the really amazing strikers like Shearer, Wright, Owen, Fowler and dare I say it Rhodes there are very few who knock them in season after season. If I was a chairman who owned a club and a striker scored 20 goals I'd sell him like a shot and look for the next one. Strikers rarely score +20 goals on back to back seasons.
So my stance on Gray stands. At £4m get him, but at £7m don't touch, especially with add ons. He might score 20 for Brentford, but we should be looking at the lad they are replacing him with. Now that would be a story.