It's helpful if you describe the structures a little - but just looking at physics - mounting them indoors does impede their performance quite a bit. Wifi is often a bit misunderstood - there's a radio signal that's let off the AP that goes bouncing around - bouncing off walls, going through some windows, etc - just a big scattered mess - but if properly focused it's actually a quite predictable wavelength that can travel through space quite a distance (miles if properly focused). Think of a MagLight flashlight - if you focus the beam narrower you can see so much further - indoor wifi is often like taking the whole head off the maglight and leaving the bulb exposed - pretty bright right around the light but doesn't go far - or you can put the cap/lens on and focus the light in a particular direction and light up something a half-mile away. Wifi isn't much different.
If you can mount two nanostation m5's where they can see each other, you'll get max speed/performance. That said, I know someone who is connected to his dad's house 2 houses over using his dad's internet and accessing movie shares and the AP's are inside the houses, pointing through windows and going through the houses in between - any RF engineer would run away screaming but it *is* working. It could be a lot better though if they both mounted the M5's outside the houses on pipes that let them see each other.
EyeofSauron - the Pico is a great device but with some limitations - its own range is amazing, but speeds over 65mbps require MIMO / multiple radios which the Pico doesn't have - it's a "single chain" device meaning it's max speed is capped by the protocol. Depending on the application it may not matter one bit - but worth mentioning. The Pico M2 HP Is also kinda awesome in that it can be flashed to UniFi as well.
