The MSI has a much better cooler and will probably be quietest. Personally, I never bother looking for factory OCed cards since you will pretty much always be able to OC a stock card to those clocks anyways (factory OCs are usually very conservative) and factory OCed cards usually cost much more which just doesn't make up for the tiny difference. Point being, I would recommend simply getting the cheapest card using that GPU with a decent cooler (which the Twin Frozr happens to be) and OC it yourself.
To your second question, the graphics card will be perfectly compatible. It will simply use PCIe 2.0 instead of 3.0 but there won't be any performance difference (graphics cards are still no where near close to being bandwidth starved). So everything is fine regarding that.
I wish i could scream this from a rooftop "DO NOT BUY EVGA UNLESS YOU HAVE A POORLY VENTILATED CASE WHERE REFERENCE MODELS DO BETTER, THIS IS THE ONLY TIME TO BUY EVGA CARDS".
EVGA does not innovate, they have terrible aftermarket coolers compared to other companies, they put zero money into R+D. What EVGA is good for is buying a reference cooled unit (because they are all exactly the same) for their warranty and customer support, which is good.
The discussion should be MSI vs Galaxy, but thats not reallly a discussion either, galaxy wins.
For reference cards: EVGA: you will get a better customer service experience from calling in for tech support to rma'ing to warranties.
For aftermarket cooling: I would say MSI has a stronger angle on this they provide a more enthusiast centered product then EVGA does as the only non reference thing EVGA does is there waterblocked cards.
So what it comes down to is what you feel you value the most the warranty and customer support or the better overall performer. Based on the first question of your original post the MSI card will pounce on the EVGA card.