founders edition is nvidia reference design for 1000 series. and they are expensive than most custom designed 1080 out there because with 1000 series nvidia finally decided to charge premium on the metal shroud that being used on their reference design. even if you must go with blower type cooler you better go with board partner regular solution which is a whole lot cheaper. for thermal and noise custom 1080 with open air will win against founder edition any day (like the G1 Gaming; unless you have super cramp build like mini ITX case). and if you want to overclock custom 1080 is definitely the better choice.
there is quite a gap between 1080 and 1070. in general 1080 is about 20%-25% ahead of 1070. with OC 1070 can almost matching 1080 but still fall quite short (and 1080 can also be OCed). but before the price cut of 1080 (AFAIK there is no official price cut for 1070) the is quite significant cost difference between the two. 1080 usually start from $600+ to $700+ while 1070 starts at $380. but now 1080 starts at $500 (sometimes cheaper depending on deal) while 1070 pretty much still cost like it was before. so for some people that extra cost 1080 have over 1070 are more justifiable now than it was before.
btw i just found some crazy deal on 1070? but the promotion will end soon. that is if you buy from newegg:
https://www.newegg.com/Product/Product.aspx?Item=N82E16814500408&cm_re=GTX_1070-_-14-500-408-_-Product
this is the cheapest 1080 i can find at newegg right now:
https://www.newegg.com/Product/Product.aspx?Item=N82E16814125908&cm_re=GTX_1080-_-14-125-908-_-Product