My Massey is rated for about the same horsepower as yours, & I handle a 7 foot box blade no problem. I also handled an 8 foot back blade with my LS R 4047 with no problem either. So, you're 46 should handle 7 foot just fine, the only drawback is that 6 foot implements are abundant and easy to find making them less expensive to purchase compared to the seven or eight foot models.
LS XR4046HC, Ariens 60" max zoom zero-turn- Cub Cadet 1050 Rider
Like TSO said, it will handle 7 ft. fine but if you stick with 6' it will be the same width as the tractor so scraping along fences and tight areas it will be just perfect. for a mower if you want to spend the extra money it would be good to go the extra width so it will lap the tire tracks.