[Civic98lx]

I apologize first and foremost if this have been discussed before and I couldn't find the correct answer.

My car is a 98 civic Lx auto sedan with 165k.
Current tires : 185/65r14 OEM

Just picked up 4 good condition 13" vx wheels for $100.. Caps included..
I am now in search of proper tires size for it. 165 is no longer available.
175 and 185 are available.. More choice with 175.

My concern is when using tire size calculator, if I'm running 175/70 it will put my speed at lower then current. Ex: 65mph now will read 62..mph with 175/70.
But if 185/70 is use, it will put the speed closer at 64 ..mph @ 65mph now..

So, what would be my best move to have these wheels fitted on my 98 lx sedan?
Will the different in size hurt my mpg between the two size?
Will it hurt compare to my current OE tires (185/65-r14)?

Also, my speedo is read 3mph faster then actual speed of car moving. I used my scanguage and cell phone GPS app to compare. Cell phone and scangauge is dead on while speedo read higher still. I don't know if this info would help or not.

Any suggestions and advice would be greatly appreciated..

Being auto I know I will not get major mpg increase, but everything little bit help, right?

TIA