I have both forks. The Surly on my surly 1x1 and the vicious on a gunnar rockhound I have.
The surly fork will obviously do the job for you. It is heavier and made from 4130 chromo. I think it makes my surly feel and ride like a tank. which has its good and bad points. Another plus.......you can run a HUGE tire up front, which I must say, is a nice option.
In my opinion the vicious fork is worth it for your ride. I would think that since you just bought a fine steel frame you would want a fine steel fork. You spent the extra dough to get a gunnar rather than a Surly frame right? Why not follow through.
It is signifigantly lighter and has a much better feel. Plus, the Surly has only one option, a 413mm axle to crown height. You can select from a few different heights from Vicious and if you are running discs get the disc only fork (it has cool cable routing guides also).
Another plus: supporting a local builder (here in NY) who employs local people and pays a living wage)