I guess its 10% difference in gearing, and you find your truck doesn't hold OD as well as you'd like...
The 10% is pretty significant, but since your hwy rpms are so low anyways it probably doesn't make much difference.
I used a pair of 10% smaller circumferance front tires for autocross on the Neon and it was very noticable, both the extra jump off the line and the extra rpms on the road. I wouldn't have run them full time, but my 60 mph rpms were 3k+ if I recall.
If you are thinking of keeping the truck for a while, I'd be tempted to do some research on LT snow tires. We have them for our vans at work and they start with 17/32 and many are only down to 12-13/32 after 3 winters(20-25k miles?). Maybe sipe them up at 11-12/32 and go for another 3 winters or use them all summer too?
Or just try the smaller studded tires and don't tell us...