If I were to the the game to marathon. I'm assuming it will take a lot longer to research my technologies, but will the units in my queue take a lot longer to produce or will the production time remain the same?
It does, but it might have a result you are interested in anyway. On slower game speeds, you can produce only, say, 20 units before the next tech becomes available and those are obsolete. On quick, you can also produce 20, and on standard as well.
However, on the slower speed, the units that come out before the very end of their "useful life" have a lot more time to go around and do things. What's more, AFTER a tech is researched, it takes more turns to field those new units (unless you saved up to buy or upgrade, both of which are more expensive on slower speeds), leaving the older units even more time to shine.
Contrary to what everyone else experiences, I find faster game speeds easier, mostly due to the speed at which units go obsolete. On a slower speed, you pretty well must keep a standing army due to the fact that after researching a new tech, it takes quite a few turns or good money to get them on a field in decent numbers.
Try an Epic or Marathon game and see how it feels. If you still feel those units stop being useful too quickly, then look to change the research rate outside of the norm for a game speed.