If you only have ONE WEEK before show, clip him with a 15 now........a 30 to 40 is almost down to the skin and you won't have time for hair growth. He'll look almost like a MOLE RAT. (If you had a few weeks, I'd say do the short clip....THEN, a day or two prior to show, run 10 blade over him to smooth things out.
Hate to tell you, this clipping won't be great for you........but if you plan to show him a few more times? Every clipping will give you an even BETTER coat.
PS: If you do the 15 blade today........Go over him again a day before the show with the 10 blade. If his mane and and tail are sun bleached, color them. And if you plan to show him again....keep him out of the sun, like we did. Good luck.