I run four monitors on my R9 280. I honestly would just try to sell the 750TI while it has any value. Multi monitor has been supported for a very long time now and there isn't much difference between running one or more off of a single card.
Different drivers have been supported past windows XP.
With the sole exception of Vista. Vista supports running more than one card, but they all have to use the same driver because it will only load one graphics drivers. Win7 went back to normal and lets you use more than one GPU driver. Yet another reason why Vista wasn't very good.