ORIGINAL: Baroncowboy

OK,maybe I can explain a few things....
First off,the higher the nitro,doesnt always mean more performance,from different points of view... What Im getting at,is not all engines are designed to run high amounts of nitro,via design...Such as most "stockers"... It really depends on the users tuning ability aswell...
Higher nitro content will make an engine startup easier,because of a denser combustion ratio,since the fuel is more ignitable due to a raised amount of nitro in the mix,which in turn causes the glow plug to ingnite the mixture with less needed heat... This is also why you should experiment with plugs,like the colder ones till you find a better match for the engines combustion stage to work most effeciently... If you run to hot a plug for example,with a higher amount of nitro,then you will more than likely have a hard time keeping it as cool as it should be,or have a hard time making needle adjustments to suit the engines entire RPM range... This is due to a little fiend known as "pre-detination" which is what causes a larger engine such as the one in your full size car to back fire... That is really hard on engines because it puts a huge strain on the parts,such as the piston and connecting rod... In Layman's terms,it puts a bind on things due to detonating before the piston reaches dead-top-center,which will eventually cause premature engine failer... AKA toasting the mil...
Also an intresting side note about a nitro/aluminium fact - Aluminium such as your engine block and piston/connecting rod is made of has an adverse effect when exposed to the chemicals in nitro for an overly long time... Like sitting with unspent fuel in the block till next time you run the engine...
Aluminum is a very soft material that oxidizes... Nitro will increase the speed of this process and should be burnt out of the engine before putting it away for the day... Oxidization is a culpret that will cause pitting and scaring on the piston.. That results in excesive blowby which causes the engine to loose compresion more and more,over time... Not cool....
So anyways about that "cooling better" thing.... Yes and No... It will cool the engine better because of nitro's "rubbing alcohol like cooling effect" The more nitro in the mixture the better it can cool...
Lubricants such as the synthetic types found in your average glow fuels today,actualy dont help cool the engine,other than doing what they're meant to do...Lubricate enough to prevent expansion/friction lock... Truth is,excessive amounts of oil in the fuel actually cause heat to generate a higher more sustained temperature... Oil is a cunductor of heat,if you will,...yet is impairitive to supply a lubricant nitro simple does not have alone...
Kinda a "cant have your cake and eat it to" deal... With that all being said,it is easier for most to tune a lower percentage nirto full,due to the wider range of tuneability curve,since there is less to worrie about overall... However yes the higher nitro can perform better as far as getting the most power outa your engine,but comes with a maintanace price... Like going through plugs quicker because of a decreaced tune tolerance which causes overheating or detonation,in turn will promote plug failer at an increased rate...
If you just wanna bash,and have fun,the best advice I can give you is to run a good quality 20% fuel... If you must have the performance for racing,then by all means,experiment away...
Another intresting fact about alot of pro off-roaders,is that they use 20% more often than 30% just for the reason its simply easier to keep running... Falls back on the old saying >
"To finish first,one must first finish!"
On the other hand,most on-roader's use the 30% since its not such a challenge to keep things running properly,due to a leveler,higher,more sustained speed, oriented race... They usualy dont have to combat idleing or lower RPM for a relivant sustained period of time,such as is more common in off-roading,not to menchen are much lighter in overall weight which allows less grunt and strain of the engine...

I hope Ive made since,but its hard to go over everything without writing a novel twice as long as the one I just wrote! lol... But if you need any specific answers gone over,I'll be happy to help if I can... Have a good one,and may the "Tuning Gods" be with you...