Its a pretty minor bottleneck. Even a used 6700 or 7700 wouldnt really be worth it since the days of quad cores are coming to an end.
For the 2600 you can find them on ebay going for under 100 USD. New they are on sale for 120 USD which if budget isnt super tight is a good price
But if you on a budget but want to get into the Ryzen platform with a new CPU to give you options down the line look at the Rzyen 1600 "AF" 12nm (part YD1600BBAFBOX) which is essentially a 2600 that retails for roughly 85 USD. They are a little hard to find since hands down they are the best budget CPU available. Couple that with a B450 mobo, some 3200mhz or faster Dual Channel kit RAM (or suffer a significant performance hit) and you have yourself a...