Sorry if this has been done before but I would like some advice on the difference between 170 & 175mm Crank length. I am approx 5'-10" if it helps?

Cheers

5mm

Sorry, had to be done.
But in all honesty, i dont think you'd really notice. I'm 5'10", and when i built my Pace, i specced 170mm Hone cranks, thinking of clearance. Ran those for 2 years before replacing them with 175mm Noirs, and the only discernable difference to me is the Truvativs shift a lot worse than the Big S ones. Ran several other bikes at the same time as the Pace, all with 175mm cranks.
An extra few psi in a fat tyre will give you 5mm difference in clearance, and the pedalling difference in your legs is negligible, (All in my opinion obviously).

When I went from 175 to 180 it felt like I was doing on a giant comedy clown bike or something. I'm 6'4 with a short body and long legs, so longer than 'standard' seems right. At 5'10 I'd have thought 175 would be ideal.

5'7 31" inside leg;

165mm on Track Bike as it's fixed, and helps with the corners
170mm on Cyclo Cross as I tend to pedal at a higher rate
175 on FS MTB as my average cadence tends to be around 70 or so, therefore more leverage (for me) is better

I've pretty much always ridden mountain bikes rather than any other sort of bike. At 5'10", they've always come with 175mm cranks. Doesn't seem to cause a problem so I've stuck with it.

When I bought a Tri-Cross last year, I was between sized. A 54cm came with 172.5 cranks and 42cm bars and the 56cm came with 175 crank and 44cm bars. Made sense to take the bigger bike as the cranks were the same as a mountain bike and the bars were closer to what I run on a mountain bike. I don't know if 5mm on the pedal circle would have upset my knees but I knew not changing wouldn't (if that makes sense).