I suggest that you go with the higest quality scope you can afford. Eventhough you may hunt only 5-10 days a season you miss a chance in the low light of a cracking dawn or a fading sunset because your scope is essentially "done" , or the image is not crisp enough to pick out that deer clearly at 300-400 yards, or the flaring in bright sunlight is so bad that you cannot make out squat ... believe me you will lament not having spent that extra $$$.

As for 40 mm or 50 mm? A high quality 40 mm is plenty good.