Conductivity is improved by the chemical removing all contaminants from your connectors. Many connectors are plated with gold which is a fairly porous metal… when the plating is extremely thin, it can actually let corrosion through to the base wire. This is often when you will lose connectivity. The DeoxIT also penetrates the plating and bonds with the base metal, usually copper, and removes all corrosion. The totally clean metal is far more conductive. Using IPA or another volatile chemical designed to leave zero reside is not the answer because it simply evaporates too quickly to remove this adhered corrosion, think of using the hula-hoe in the garden - you are just taking the top of the weeds or in this case corrosion and leaving the root. With data speeds as high as they are, this “root” oxidation is enough to cause a intermittency or possibly a failure of the entire application. The fairly small amount of DeoxIT left on then part seals up the plating, but when a connection is made, it is displaced, allowing pristine metal to metal connections with DeoxIT sealing the around the connect point. This provides you with the highest possible connectivity.
I understand it can be confusing as to which version of DeoxIT to use. Basically, first decide how best to apply the DeoxIT for your application: what is best/easiest - a spray, a wipe, a pen, a needle oiler or a brush. Whichever is easiest to use and works to get the DeoxIT on the appropriate surface is the one to go for!
As to the strength of the DeoxIT solutions, 100% versus 5%, it depends on the application. If the equipment is vintage, created before 1980, use the 100% solution to be safe - newer propellants and solvents do not always agree with older materials. Also, use the 100% solution when you want the DeoxIT to go on thicker for extra lubrication.
The 5% solution uses a propellant and carrier solvent which provide a flushing action and remove surface contaminants like dust and other debris, and then those chemicals evaporate. This is great for getting rid of contaminants other than the adhered corrosion. Once the carrier solvent and propellant have dissipated/evaporated, you have only DeoxIT left on the part. This will remove the adhered corrosion over time, increasing connectivity, protecting your connectors and increasing the life of your equipment.