The quality the the thermal paste does affect temperatures. Which doesn't mean you need to get something super expensive. I've used Geilid extreme with good results.
Application and heatsink make more of a difference than the paste. As far as application goes, just don't use too little (or way too much) and ensure your HSF is making good contact, the pressure takes care of the rest. There are plenty of videos and articles out there about different pastes and their performance. A lot of them will come up with different #1s but there will be a few brands that will consistently show up near the top. Pick one of those.