Well let’s see. To make use of Highlander attribute you need to be able to crit. To able to crit at 280 you need to have 100 crit rating on average just to have 0% crit chance (someone correct me if I’m wrong). To get that you need 100 Dex and then crit gear and gems.
Say you’ve got 2:1:1 Str:Con:Dex ratio going, you’ll end up with 310:100:100, that’s 150:75:75 points invested. You would have 310 crit attack as a base, which would convert into 155 extra crit attack, so 155 damage every crit. You still need to crit to get the benefit, I’m not fully aware of all the crit rating items but you would roughly have 25% chance to crit.
Now you could put the 75 points into Str. You quite possibly won’t be critting at all, so highlander attribute will be useless. However, you now have 470 Str instead of 310. That’s 160 more than when you had 100 Dex, which translates into 160 extra damage on every hit, 100% of the time.
Question is can you get enough crit gear to overcome the negative crit rating that you would have at 280. You almost definitely can but how much would that be I don’t know. 2 Sissels will net you 74. 3 crit gems in your weapon would net you 276. Whoa you say, that’s going to be a 37.5% crit chance! That is if you level the green gem to level 10, which would take some dedication. You most likely have them at level 5 or 6. That’s 96 crit rating with 74 we have from 2 Sissels you’ll get 10% crit chance. It’s not bad.
Bottom line is it seems that Highlander will net you 230 extra damage damage per crit at 280 provided you can get the gear. So ultimately, it does give extra DPS but at the same time 230 damage, 10% of the time is not that great. That’s just 23 extra damage every hit, GungHo is better than that. Obviously it goes up as your crit goes up.