ORIGINAL: mobow

Ok, I went to bowjackson.com and punched in some numbers. All things being equal, except arrow weight and speed, here are a couple results.

These first numbers are a 355 grain arrow, flying 318 fps.

50 yards; 297 fps w/ 69 pounds of KE.

Here are the same results, w/a 490 grain arrow, flying 282 fps.

50 yards; 268 fps w/ 78 pounds of KE.

The light arrow slowed down 21 fps and lost 10 pounds of KE. The heavy arrow slowed down 14 fps and lost 8 pounds of KE. So, in short, the heavy arrow retained 7 fps and 2 pounds of KE over it's lighter brother.