For all of its inaccuracy and the extra bells and whistles that aren't needed, Shandara's Hunter spreadsheet on the ElitistJerks forum (elitistjerks.com) is a good tool to use to compare the value of items and potential items. What is an upgrade will greatly depend on what you are wearing now, your talent spec, your shot "rotation" (more of a priority system now), your pet, and whatever buffs are present in your raid.

The sheet is not accurate, but it's inaccuracies are proportional, meaning that you can still use it to see whether Envoy of Mortality is better or worse than Siren's Cry, and be reasonably confident of that determination. You can also play with shot priorities and find a good combination without spending hours in front of a training dummy. Just don't expect to reach the DPS that the sheet predicts, or any of the shot values you see in raids to match what you see on the spreadsheet.

If, like me, you don't have Microsoft Office, the basic features do work in OpenOffice, though there are a few glitches as Shandara tries to get fancy with it. Just don't expect it to pick out your gear for you and spoon feed it to you, like it will do in Excel.

Perhaps the most annoying glitch is the lack of sorted gear selection fields -- using Excel, the gear selection is sorted based on its relative upgrade potential; not good if you have specific items you want to test, instead of "Uhh, which pretty purple is good for me?". And the latest sheets seem to have the validity settings glitching in OpenOffice. All of that can be easily fixed, but it's still annoying. But the sheet is still a useful resource.

"The Hunter's Lodge" has another sheet that spawned from the same source that Shandara's sheet did.