While renders to DVD are impacted significantly by how powerful your GPU capabilities are, renders to h.264 (best for YouTube per Ann Bens) are largely impacted by how powerful your CPU is. So most likely, changing to a more powerful GPU, or adding an additional GTX card (CC supports more that one card for hardware MPE), would probably not help you much at all.
While doing a render you can check to see if your CPU(s) are working hard (over 80% for all cores as measured with task manager). If so, that is a good indication that you are "CPU bound" (CPU is your weakest link) for this particular workflow (renders to h.264). If however your CPU is not working very hard, it could be that more RAM could help you some. 8GB is not that much these days, particularly for some of the higher pixel count media formats.
Regards,
Jim
You English is OK. I would only say when you say "doubts" the proper English translation is "questions". Is you native tongue possibly Spanish or Portuguese?