Ha ha, im told that fish stuff is all me and i will not be getting anything fish related for christmas...bummer.
10x filtration is recommended for goldfish because they are dirty fish, poop machines and mess makers. Think about this...the more or less water you have passing through your filters equals more or less ammonia that is being converted into nitrite and then therefore nitrate.
Because goldfish create more ammonia per fish than lots of other fish they require a higher filtration rate than other fish, so the faster the filtration rate the faster your ammonia gets converted and becomes less toxic.
If you are talking about 2x the filtration rate on your 70 gallon with the two small goldfish then thats a different story. That tank is really understocked therefore it will take a longer time for nitrate to build up.