mods are a funny thing. by themselves they may be effective but when done together they tend to work much better. First thing to get is a slip on. A full exhaust is only around 2 to 4 hp over a stock system and the 4 hp is with a heavily modded bike. NOw the vacum hose trick or Pair mod as it is commonly known is a very inexpensive mod. you have to buy a vacum hose that will cost you $5 from any autoparts store. You need a 1/2 inch T connector and your choice of plugs or silicone. The advantage I really noticed out of this is the way my throttle response is. I have a friend with a stock 6r and immediately you can feel the difference.. It just seems to rev that much faster. The pair mod accomplishes this by using the flow by gases in the exhaust manifold to suck out all the air from the crank which creates a vacum enviroment. Now the air filter and Jet kit should usually be done together. By themselves they will not give you optimum performance. Together they are great. People debate stock over K&N air filters but I personally like the K&N. I used a Factory Jet kit. The write up on Factory is less hassles. A couple of the other jet kits out there are more tempermental...now the gear changing and ignition advancer are both mods for increasing acceleration. THe ignition advancer allows the bike to hit harder at a lower RPM. Again comparing my bike to my buddy's.. I can pull away when we both hit 4000 rpm where as he hits around 6000. Gearing is a personal preference. I suggest against going down more than one tooth in the front. Just one tooth is very noticeable and will cost you around $20.. I paid $19 for mine. Easy to change and a very noticeable difference. I do find myself reving out quicker but not enough to be a pain in the ass. I have a friend that went up a few in the back and down one in the front and a harley can rev longer. HOpe this helps.