On their website, they don't have the steel in 525 for the rear. Says "Rear sprocket not available for the selected bike & pitch". I'm not buying an aluminum Vortex. I've heard lots of negative things about them.
I would run a 15/46 over the 16/49, that's a big cog in the back, and I have found keeping a 15 up front with rear between 44-47 have been sufficient for short (barber/Talladega gp) to long (road atl/roebling) tracks this year. Hopefully when I'm faster at road atl next year I'll need a 43.