How bad are your existing shocks currently? Few things are more important {like brakes and tires} so if the current shocks are shot spend the money and get the Heavy Duty Bilstein's. They are lot cheaper {and IMHO, better than the Koni FSD's but opinions certainly vary.}
The Bilstein's are about the same as the top of the Line Monroe's and others as well. I replaced the original shocks on my 2012 E-350 at 33,000 miles with the HD Bilstein's and wished I had done it a lot sooner. Day to day you tend to not notice just how bad your shocks have gotten as the change is gradual. But, put a new set of quality shocks on and WOW, what a difference that you will notice immediately.
Bottom line I highly recommend the HD Bilsteins... they are worth every penny!
:C