Linus is an idiot. Period.
As far as your fan configuration is concerned, that is a very minimal cooling configuration however increasing the size of one of the fans cannot "hurt" anything. Yes, it MIGHT create a positive pressure arrangement, but that will ONLY cause you to have better dust suppression. It's not going to reduce your cooling capability at all. It might actually increase it since an older case with only room for an 80mm exhaust fan will probably have many gaps and holes for air to escape from so some amount of the added air pressure is going to find it's way out, taking some heat with it.
Optimally, you would want equal air pressure or negative air pressure for the best cooling. As follows.
High static pressure fans are desirable for all intake fans, radiator fans or heatsink fans. All of those types of fans will usually encounter significant resistance to airflow, so having fans with higher static pressure is desirable in those applications.
Exhaust fans do not face much resistance, so using fans with high static pressure is not necessary in those locations, however, USING them will not hurt anything either. Technically, you generally want fans with the highest CFM and highest static pressure you can reasonably afford to purchase for intakes, heatsinks or radiators. Exhaust fans, the static pressure is not very important but high airflow (CFM) is generally desirable.
For most configurations 2 x120mm, 2 x140mm or some combination of the two for both intake and exhaust are sufficient. WHEN possible, using a 140mm fan is much preferred as you are able to move an equivalent amount of air as a 120mm fan at a lower RPM resulting in a lower overal noise level.
Negative pressure configurations offer the BEST cooling performance. Positive pressure configurations offer dust suppression. Neutral pressure, with an equal, or nearly equal amount of airflow coming in as what is going out, offers a good solution that meets both types halfway. This is the MOST recommended configuration. If you want the best cooling performance, then you might not only add another exhaust fan to that top rear position like I said, but make sure it is a high CFM model AND also maybe replace the current rear exhaust fan with a model that has a higher CFM rating as well.
BeQuiet fans are only good in regard to noise levels, and that is only because they tend to run their fans at a maximum RPM that is significantly lower than most other comparably sized fans. They are good for systems that don't need great cooling and silence is more important, although you can technically do that with any fan by adjusting the fan curve in the bios and capping it at a speed that is acceptable.
If performance is more important, I would stick to fans by Noctua (And yes, they have black models now so you are not stuck with baby poop brown), Thermalright (Not to be confused with Thermaltake) or even possibly the EVGA FX 140 or 120m fans which move a lot of air but are a bit noisier than these others. Corsair Maglev fans are also fairly good.
However, in your case, with an older chassis that only has an 80mm exhaust, if you cannot install a 120mm fan in that (hopefully) rear exhaust position, then there's not much you can do. I'm guessing this is probably a case with a top mounted power supply, or no? What IS your case model?
What are the rest of your hardware specs?