If your Fox Body is still stock and you intend to keep it that way for the foreseeable future, then an OEM replacement radiator will do the trick. If the stock radiator was able to do it up until now, a replacement OEM unit ought to be able to continue the job, no problem. If you have done some modifications or plan to later down the road, go with a performance radiator. It is generally accepted that with aftermarket modifications that the 5.0L engine will run hotter.
Aftermarket performance radiators for Foxbody Mustangs are usually made of aluminum, which dispels heat much better than the stock construction. Furthermore, they usually are bigger and beefier, with larger cores providing more surface area to draw in more air, thus better controlling temperatures. The stock piece is a 2 core design whereas quality aluminum performance radiator usually has a minimum of 3 rows, again better to dispel heat throughout coolant circulation.
One other thing to take into account when purchasing a radiator is transmission type. A radiator intended for a manual transmission usually differs slightly from that intended for an automatic car because of the extra transmission cooler needed for the automatic transmission. Some radiators are universal, but not all, so just keep that in mind.
Now, one drawback to aluminum is that it can be somewhat brittle. Road vibration and bumps can stress the radiator and cause it to crack and then leak. This is why it is very important to purchase a quality radiator with quality welds. A poorly made radiator will let you know sooner rather than later, sometimes leaking right out of the factory!