990FX

Apologies for the delayed answer.

1. Having your fans on auto is fine and probably explains the temperature being similar in Prime95 and web browsing and doing other stuff. While your CPU cooler seems to be more than enough to cool the CPU at your current settings, please remember that you should also monitor the socket temperature, which is probably a bit higher.

2. Using the BIOS OC is probably fine when using the 5% setting. There's no guarantee that it's stable, but there's a reasonable chance it is - and you can check it using Prime95 and RealBench. Is it worth using? That depends on what the settings actually are. Sometimes those BIOS OC settings set the RAM to very low speeds - probably in an effort to make life easier for the memory controller - which may not be what you want if you are doing some of the (few) things that RAM speeds actually has an effect on.

Based on what you've told, I'd skip using AMD Overdrive altogether and run the CPU on stock BIOS settings apart from the core unlock feature. Those two extra cores should already give you a nice performance boost for video editing and in gaming your CPU is not really a bottleneck at the moment. If at some point it starts to feel like you'd like to get even more out of your CPU, you can then look into overclocking in more detail. Start with the link to Dolk's guide I provided earlier and just google anything you'd like to know more about. You can of course try the BIOS OC settings as well, as something higher than 5% may also work (remember to test for stability). Just remember that if you decide to overclock, you should be willing to put some time into it, even if you're not trying to push your system to the limit. Slow and steady will give you the best chance of ensuring stability.

P.S. If you want to upgrade your GPU on a budget of 100$ or less, I'd consider getting an AMD Radeon R7 250X or an NVIDIA GT 740. There are different versions of each from different manufacturers (with varying prices), so you should spend some time looking at reviews, youtube videos and comparing specs so that you'll know what you're getting. Availability may also be an issue. In general the R7 250X should be better for gaming while the GT 740 will consume less power.

Xaltar definitely has a point. If you are willing to buy used, you'll have access to better performance for the same amount of money. New or used, just make sure you have some idea of what sort of GPU fits your needs and your current hardware (power consumption, required power cables, the amount of memory the GPU has, the physical size of the GPU etc.).