Having had both, here are my views.
The M70 is simpler and has fewer moving parts. Therefore ultimately its probably less likely in the long term to give problems. Its a good rifle but the R8 is something special.
I have had no issues with my R8 and I have had it absolutely caked in dust and also soaked wet conditions. No problems. It just feeds and shoots.
I have no experience with it in sub zero conditions however.
I no longer have an M70 and my R8 is my favourite hunting rifle. To me its the most instinctive rifle I have owned to hunt with. That is, once one gets used to the straight pull system and the decocking system (safety). And that does not take long.
The straight pull is so easy to use and very fast to reload, if that is required. Feeding form the mag is flawless.
The tang type decocking system is the best safety system that I have seen on any rifle thus far. When its decocked it CANNOT fire - its a physical impossibility and therefore its the only rifle thats genuinely safe to walk with a round chambered. The new Sauer 404 and the Steyr SM 12 now use the same system and I can see why.
The only problem I see with this decocking system is if one has arthritis in the thumb as it requires considerable pressure to recock the firing pin spring. It certainly cannot be done by accident!
Then there is the shortness, the handiness, the multiple caliber option, the ability to transport the rifle in a small case etc etc.
Just the price one has to deal with!
Last edited by mlg; 10/24/15.