You say a 400 is too heavy. By that I guess you mean mass weight; you're looking for more speed? Actually you would probably be better served using a .340 spine than .400. So in Easton arrows you'll be getting even more weight.

If what you want is more speed then get on the different arrow-maker websites and compare. Easton has their Litespeed series. GoldTip has their Ultralite series (very good arrows). On Gold Tip's website they have a link under "products/build your own arrow" that you can see what your arrow would weigh finished. Whatever you come up with just make sure you get the right spine and keep your total arrow weight to at least 325 grains. To check for spine you use their spine charts. Also, the GoldTips come in three different grades (tolerances); Expedition (Lower price), XT's (middle) and Pro series. Depending on your pocketbook the XT's are the better buy.

Hope this helps