The 3930 is 45 PTO HP, the 4630 is 55. The 3930 and the 4630 were both turbo'd in the later model years, primarily due to emissions regulations. Both were built with 192 and 201 cid engines during their model runs, with the 192 cid engine being turbo'd in the 4630 and then in the 3930 near the end of it's run. I'd go with the 4630 for the power advantage as well as it being offered with up to 16.9 x 30 inch rear tires while the 3930 was maxed out with 14.9 x 28's. The 4630 would be better for baling hay in my opinion.
So how did they get 10 more hp out of the same engine? It looks like 4630s run a few grand more on average. Is this accurate in your opinion?