What Is The Best Big Bore Kit For The Trails?????

WHAT WOULD BE THE BEST BIG BORE KIT FOR TRAILS AND OPEN FEILDS WITHOUT THE BIG $$$$??? I WAS THINKIN OF THE 416 BUT I WANT YOUR OPPINIONS.
THANK
THIS IS FOR A STOCK 400EX

[stocktires]

for a stock 400ex, i'd say the 416.
it revs quicker, you'll still have bores left on the sleeve, and It will stay cooler.
But I wouldnt get a bigbore unless i had a muffler (slip on will do just fine).