Walking for Fitness

I've recently started to add walking with a weighted vest as part of my off day programming.  Walking in and of itself is a nice way to recover from heavy CNS type workouts.  Adding in the weighted vest makes it a little more challenging but not enough to hinder recovery.  

I'm currently doing 20lb, the max in my vest, for 30 minutes.  The goal is to get to 60 min and pick up a 50 or 60lb vest.  

There are some studies that show that walking with a vest burns more calories and its effect on a few other variables, like ground reaction forces.  Effect of Weighted Vest. 

My goals for adding this in was to incorporate some more low intensity but constant activity.  Strengthen up the foot/calf muscles.  I'm wearing a more minimalist style shoe, not vibrams, but not tanks.  Burn a few more calories during the week.  

Does anyone have any suggestions on a brand for weighted vest in the 50-60lb range?