I was only referring to the fact that one of the fastest techniques in existence, Kirin, happens to be a lightning release technique.
Now, I would guess that the relationship between fire and lightning is the fact that both can cause severe burns, and both require more chakra than the average technique. Also it would seem that most techniques of these elements are created by your chakra, rather than being manipulated by it, meaning that these techniques can be used at any location, regardless of the surrounding environment.
If using Earth and Lightning, i would probably use the earth release techniques to defend myself from attacks, and then switch to lightning release to attack through my own prior defense, as lightning can easily attack through earth, giving me an added element of surprise.
As for Lightning and Wind, i think that using wind to make an opening, or even to block and disperse another wind based attack would make it possible to strike with another lightning release attack.
When it comes to physically combining the techniques to strengthen lightning... i'm not exactly sure how that could be done, as earth would naturally absorb the lightning rather than strengthening it, and wind would naturally insulate against the lightning, i don't know how i could really combine them.
Well, Kirin is a tricky situation, as it's not Lightning Release, but rather the manipulation of Natural Lightning. But we shall get to there in due time.
Now, first of all, the Bold, great observation. That is indeed correct.
I guess what you're trying to say, when you analyzed the "burning" aspect of each element, is that they're both Energetic elements, while the other 3 are more substantial elements. Combinations of the two will, of course, create more energetic outbursts, either accelerating their speed, or their temperature, or there volatility. Indeed that is. But also because they're both energetic elements, it's harder to combine, as there aren't any actual substance through which one can infuse the other. To bypass that, I found that using techniques that force both to coexist, especially in high motion, is the best. So vortex-type techniques are the best for combinations (This is true for most elements, if not all). Since you'll be making both elements rotate in the same speed and manner, they're forced to interact, without canceling or overpowering one another. What should come out of that combo is an highly energetic and volatile "tornado" at great temperatures (Without exaggeration, of course). Likewise, we can look through a more tactical eye. Fire's strength is Lightning's weakness, so if you use a fire technique, that would make the opponent more hesitant in using a Wind technique, if you then follow with a Lightning technique, it will give little chance for your opponent to be able to block.
I like your rendition of Earth x Lightning. That element of surprise is always great to use. Another thing you could do, though, is charge lightning through the ground, making it graze and friction through the ground, rising dust and debris in a wave, following the lightning. It will sacrifice the speed a bit, but it will add a more substantial attack to the lightning, as the enemy is hit with it and with flying rocks and sand.
Wind x Lightning is not very good. At the light of the new knowledge I shed, come up with a better answer.
PS: I didn't quite get the part where you said that Fire and Lightning require more chakra. That's not really true, they require just the same amount of chakra as any technique of their rank