highest lvl is 37 so I am not sure what it is best used in, but it is damn well near perfect.... any ideas on how much it is worth?

It's hard to say 'this item is worth x', it all depends on the buyer. The mod's level range is pretty poor seeing as it's for midgame and most people won't spend too much while levling. I would never spend more than 200k on an mod at that range, but there might be someone out there ready to pay way more. I'm quite greedy..

Look for someone stupid enough to be building a crit based gun guardian, this'll be perfect for them.

onslaught/blessed onslaught was the dev's way of saying crit gun guardians are completely viable and totally worth vomiting points into accuracy for mediocre single target damage

If it fit lvl 50 wep and was 3% it'd be godly

well it sold on auction house for 400k after a few days, think I got a good deal?

yes