16.9-38 vs 18.4-34 tires

I'm looking at buying JD 6420 4wd with loader. My only concern with the tractor is that it has 16.9-38 rear tires instead of the 18.4-34s that you see on most 6420s. The neighbors 6420 which I have been using for the past year has 18.4-34s which seem to be a nice size for that tractor. I'm worried that I might not like the slightly taller but narrower 16.9-38s.....especially for loader work. Moving bandit bundles out of the field will be the main job for this tractor but will also likely mow and/or rake. When it's not in the hayfield the tractor will likely be used to pull a notill drill some and do odd and end jobs. Will the 16.9-38s okay for these uses? Will I have less traction?

16.9-38 vs 18.4-34 tires