I don't think you can really compare or guess at this as technology in the fantasy universe is artificially retarded by gw.
As an example if you take sigmar as basic iron age the amount of years that have passed far outstrips the numbers that have passed since our iron age yet the Empire is barely reaching the equivallent tech of our rennaissance era.
Other races have fared even worse The highelves haven't advanced technologicaly since the war of the beard which equates to the humans neolithic era and he Dwarves have not done much better only using blackpowder on a level with the 15th century.
The main reason for this is to keep 40k and fantasy as 2 seperate games systems so the chances of the Empire ever reaching steampunk levels are unlikely.
Factor in aswell that in general war breeds inovation the Empire should be miles ahead of us as they've been under constant threat of war of some sort or another since Sigmar.
Neil answered well, but I would add to that the fact that magic and monsters are abundant will also presumably have an influence on technological advance. Why push manned flight technology when you can leap on a dragon? What use is advance to High Elves when, other than demons, life is pretty spiffy?
Also remember that nature is sacred to the elves, technology inevitable defiles the green verdunt lands. If your an elf your armies are arguably still the most powerful, your navy rules the waves, why risk weapons that can kill the user as often as the enemy?
High elf mages far more capible than a cannon, or morter, sure the pyrotechnics look impressive, but is that a comet in the sky?
As far as war leading to innovation, thats only true to a certain extent and really only in the modern era. Look at the roman empire, it was constantly at war, yet technology declined. The middle ages technology improvement was so slow it may as well not have happed. Mass production in the C18th lead to the boom of ideas. Until the empire uses mass production war is an incredible drain on their resources and creative ideas. Everything is hand made so each is unique and unrepairable
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