Well, I don't think a comparative study can be done. We know that Guru Gobind Singh ji gave Guru gaddi to Sri Guru Granth Sahib Ji so he, if not agreed with, then at least respected the teachings of the other gurus. He didn't leave behind any teachings that we can use to study, whereas Guru Nanak did.
About the 5 ks, those served a practical purpose. Kes and Kirpan were direct insult to the Mughal law. Kachera was more practical on a battlefield than a dhoti. Kangha was used to keep kes clean, very practical. Kare can be worn like armour and serve as brass knuckles in hand-to-hand combat.

We know both Gurus fought against injustice, oppression, etc. By the time 10th Guru ji came around, it had become worse. Guru Nanak dev ji fought with pens and his words and Guru Gobind Singh ji picked up the sword. Again, it was situation dependent. But if you recall the zafarnama then you know that this is more of a similarity.
They both rebelled. Guru Nanak touching achoot is similar to Guru Gobind Singh keeping a kirpan or wearing a kalgi.

I dont think there was any evolution. the gurus kept us going and got us through tough times. They stopped the human Guru trend when they thought it was right. Their teachings were consistent with each other, although, they may have been different in their own views, thoughts and actions.
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/sikh-sikhi-sikhism/41-teachings-guru-nanak-dev-ji-guru.html

So again, Guru Gobind Singh ji really did not leave anything behind, which we could study. What he gave us (K's) were very practical at his time, 2 of them were there to rebel against the authority. The others served a purpose in "rough" times. both Gurus, fought against the same thing. The way they fought depended on the situation.
So I don't think their teachings were different. Perhaps their personalities were. Everyone is different somehow. But the gurus made sure that they left a consistent message for the Sikhs.
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=41


Talking about Gurus individually, I read some eye witness acounts on a website a while back. it stated that Guru Arjan dev ji was a strict vegetarian whereas his son, Guru Hargobind was an avid hunter and ate animal meat. If anyone knows where that is from please let me know. Thanks