Well depends on which 970 you get, if you get a card that isn't the blower style and dumps heat into the case then having some extra airflow around the gpu's can help out quiet a bit. As for leaving the 570 for physx, well you might not notice much of a difference because a single 970 at 1080 will pretty much chew up anything you throw at it and not every game will be using physx. 
 
As far as msi vs evga 970's. In terms of gaming performance there's really not going to be a meaningful difference unless you get models that have a large difference in clock speed. That being said, the msi does have 2 extra power phases, which means it has the potential to overclock higher, but from what I have read there is still not significant difference in overclocking ability when using above ambient cooling(air, non-chilled water), it might come into play in bench marking with cooling like below room temp water or ln2. The air coolers on the msi are also a bit cooler/quieter. So overall the msi does have a moderately better build quality but no real measurable difference in performance for gaming other then the msi has slightly better temps/noise. Pretty much all manufactures evga and msi included have been having problems with coil whine. 
 
There has also been some talk about the TDP limit being lower on the evga card causing it to throttle sooner so again it *might* not overclock as high as some of the msi cards. Its still silicon lottery in the end. Some people have been saying that hitting this TDP limit is cause stuttering/tearing in games, honestly I do not have a gtx 970 I have the gtx 980 but out of boredom I lowered my tdp limit so I would hit the limit and I had no such problems. I do not see how this would cause stuttering as the card was designed to do this but I do not have gtx 970 and can not test this personally. I have some concerns if it is the card itself causing these problems or something else. 

Thank you! Very helpful replies. Do you think that gtx 970 plus a gtx 570 for physix Will create bottleneck with a i5 2500? I made the mistake of not buying a k so no ocing