And by all means, if you believe another version besides these two is much better and warrants the price increase (if there would be one), then definitely suggest it. Make sure to consider shipping prices, as well.
It's a bit more, but it's so much better because it comes overclocked so you don't have to worry about taking a risk and invalidating a warranty. Also, the Sapphire has two fans, where as the two GPUs you linked only have one.
I would also recommend a non-reference cooler model. One of the great upsides of the 7850 is its huge overclocking potential (some cards can push above 1200 MHz, which is like a 40% overclock!). You'll have much better OC luck with a better cooler.
Of course, if you don't want to overclock yourself, it's good to get a factory OC model, though for this particular card, I'd really encourage you to OC. Then again, if you are truly committed to not OCing, just get the cheapest 7850. Brands don't matter much.
That Sapphire is out of stock on Newegg, I definitely would have went with it otherwise. It's so much more on other sites, though.
I'm not sure what a non-reference cooler model is, either. So please simplify most of what you're saying, since I'm generally ignorant of anything specific when it comes to comps, I only really know part performance and how to build decently.
Sure--"non-reference" means a design for the cooling on the card (the fans, mostly) that is something other than what AMD or nvidia suggested on their original model. But usually people just use it as shorthand. Reference coolers tend to exhaust air out the side of the case (axial cooling--along the axis of the card). This keeps the inside of the case cooler, but it's harder to do well, so it results in worse cooling for the actual GPU. Non-reference coolers tend to be open air models, i.e. they exhaust heat into the case, so you need good airflow within the case to make them work. But they give better cooling performance for the graphics card in general.
Basically you can tell if it's non-reference by looking at the card: it will likely have much more surface area devoted to two or more fans, instead of just a single fan and a lot of plastic casing. The non-reference cooler cards tend to be at least $10 more expensive, but sometimes $20-40 more expensive if the card is also overclocked right out of the box.
You can overclock basically any modern video card by using either AMD's own driver suite (Catalyst), which you will have to have as part of the software for the card, or using a specialized utility such as Trixx or Afterburner, which are pieces of software made by Sapphire and MSI. You should really consider overclocking if you're getting a 7850, because it's a great card for it (akin to the 2500k in the processor sphere).
Yeah I've wondered about those two particular cards too. The only reason the OC model might be better is if they "bin" their GPUs, i.e. they test the parts they get from AMD and put the more overclockable ones in the OC model and the less overclockable ones in the non-OC model. Because the OC they apply is fairly modest, I doubt that they bother doing that, but I can't say for sure. Anyway, though, I doubt it's worth the ten bucks even if they do bin--that only matters for pushing the upper upper limit, which most people don't do. So get the cheaper one.
Well a 4.0 GHz OC on the 2500k is easier than falling off a log, and the same applies for 4.2 pretty much. Past that you might have to mess a little more with voltages.
Think about it this way, though. The overclock on your 2500k will have very little effect on gaming performance. Overclocking the video card could have a dramatic effect. A 20% overclock on the video card will, in many games, yield a 20% bump in FPS. And buying a 7850 to overclock to 1GHz is basically no different from buying a 7870 (which is a very similar card but runs at 1GHz). So put the effort where it will make a difference, IMHO.
You should be able to push it up to 1GHz without a problem. Many reviews have gotten 7850s up to 1.2GHz clock on core and shaders and an additional overclock on the RAM (past 5GHz). You'll just have to try a few iterations. It is really not likely that you'd permanently damage the card doing this; at worst, you just have to scale things back down once you start seeing artifacts.