Having played both Svirf and Assassin Villagers (along with a host of others) I found the following things to be true:

1. When you're a Svirf, mages are exponentially more wary of your intentions than any other race. I found that pre-applicant most mages would go out of the way to not be in the same area as me, and as that character would not lie for his first kill it was much, much more difficult to get a kill with a Svirf than with a Dwarf, Arial, etc.

2. It's not an Assassin's ability to see invisible that gets him the easy kills. It's hide. Because of this the easiest class to get lowbie mage kills with is Thug Thief. I had nine mage PKs with my Thug and I'm not a very good PKer now. In 2009 I was terrible, yet still managed to get those nine kills.

So, it might seem like Svirfs and Assassins have an advantage, but I'd put forth that the Assassin's advantage has nothing to do with heightened awareness, and a Svirf is actually at a disadvantage.