Hard Ground (HG):

Hard Ground cleats are shorter.  They may have an additional cleat in the ball of the foot or along the outside.  They are generally made of a plastic material to provide some cushion.  In general, they are molded into the outsole and can not be removed or replaced.  HG boots provide poor performance in wet or muddy conditions because they tend to clog.  They may not penetrate the surface deeply enough to provide any wet traction.

Firm Ground (FG):

Firm Ground boots are a mid-level design.  This is the most common cleat pattern found in stores and the only one available at lower price points.  The cleats are generally plastic, but my have a metal tip on high end boots.  In general, they are molded into the outsole and can not be replaced.

Soft Ground (SG):

Soft Ground boots are designed for muddy conditions.  They also work well in longer grass and in snow – but not ice.  They have much longer, but fewer studs.  Typically, there are only two at the heal and four to six at the toe.  Soft Ground cleats are generally removable and may come in a variety of sizes.  The less dense cleat pattern is designed to enable deeper penetration by the cleats and prevent clogging.

Tunit:

Assuming your foot will fit the F50+ shoe (very narrow), the adidas Tunit system may seem like an ideal combination.  The full system includes everything required for three different boots and the ability to mix and match for the ideal combination (and the ability to change boots at half-time.  Given that you can purchase replacement parts, this would seem like an ideal situation.  However, I have not had the opportunity to test these boots.  Feedback regarding the Tunit system, or any article, is encouraged.  I may post your comments after review.