As mentioned above, I use a corrugated plastic political sign cut to fit so that it covers about 80% of the radiator. Makes for much faster warm-up times and allows the tractor to maintain operating temperature during the colder days doing lighter work like powering the wood splitter. Runs much smoother and more efficiently than when it ran cold without this setup.
I also work it hard with this setup plowing our 1/2 mile driveway and skidding logs, never had an issue with overheating. Like many other makes/models my 4540's cooling system is built to keep the engine cool while pulling implements in 100* heat, and as such is way overkill for the type of winter work I use it for. Without the radiator blocked off it would never get up to full operating temperature in the winter.
OP, I certainly wouldn't hesitate to block at least a portion of your radiator, I've had positive results from doing so.
Edit: On a side note, thought I'd contribute on this as well. I use the winter front religiously on my 2013 Duramax during the colder months, greatly improves warm up times and operating temperature conditions. Driving on cold days (less than 0*F) without a load I can hear a noticeable difference with how smoothly the engine fires. With the winter front off it'll struggle to reach operating temps and run clattery (not sure on the proper term for this) for the duration of the drive. Winter front on, easily reaches and maintains operating temps and runs properly smooth. However, I always remove the winter front for towing, no matter the outdoor temperature. The added load provides enough resistance to properly get the engine to operating temps and high EGT's aren't a concern with the cold air flowing over that intercooler.
Another important point, is the difference that an intact emissions system can make. The reason why you don't see many new trucks running winter fronts (semi's and pickups alike) is because the Tier 4 Emissions equipped exhaust systems are much more restrictive than their older, free-flowing, non-emissions counterparts. This added resistance greatly improves warm up times and the ability to maintain operating temps on cold days.
For example, when my Duramax was new (i.e. "stock") I never had any need to use the winter front even on the coldest days. Once it underwent some mechanical weight loss surgery that resulted in a freer-flowing exhaust system, it then started needing the winter front for the cold season.