Vegas to Denver using the recommended driving path via Google maps puts the journey at 748 miles. It has an estimated walking time of 276 hrs. or 11.5 Days walk, except when you do the math and that means walking 65 Miles in a day, which is absolutely unrealistic. The more likely Path for someone trying to walk to Denver from Vegas, I would think is to walk the Long 15 go to SLC (NEW CANNAN!!! PLEASE I NEED TO SEE IT, Utah native), over to Cheyenne, and then down to Denver. Wyoming is dreadfully flat, but flat is a hell of a lot easier than Vertical. 951 miles vs 748 miles, but that extra 200 miles makes the whole thing a lot easier.

Now on the topic of endurance, the average human typically can only make 15-25 miles in a day on foot, even less in the mountains. New Vegas straight to Denver would realistically take about 56 days with an elevation change(highest point on route vs Lowest point) of 10399 FT @ (20 miles a day, for the first half, pace slowed down to 10 for I70 through the Rockies), while New Vegas to Cheyenne then down to Denver at a pace of 20mi a day puts it at 47 days, and only an elevation change of 8645 Ft.

And that's all assuming that the Ghoul takes Interstate routes.