This is about as top of line as you can get without just being stupidly expensive.
ASUS SABERTOOTH Z77 http://www.newegg.com/Product/Product.aspx?Item=N82E16813131821
You can go with this too, but there's no real reason to IMO.
ASUS P8Z77-V DELUXE http://www.newegg.com/Product/Product.aspx?Item=N82E16813131818
After that, things get really expensive. The absolute top of the line.
ASUS P8Z77-V PREMIUM http://www.newegg.com/Product/Product.aspx?Item=N82E16813131850
There are much cheaper options, but you asked about top of the line, so that's what I showed you.
Now as far as 2500K vs. 3570K, that's totally up to you. The 2500K can OC further, but the 3570K is faster at stock speeds.
And don't worry about the iGPU in the 2500K/3570K. That's a complete non-factor for OC potential or anything else performance related and is actually a good thing to have if your dedicated GPU ever stops working, so you can do some troubleshooting (and so you won't have to go without a computer while you wait for a new GPU, should that be needed). It absolutely will not interfere with the dedicated card, as it will be disabled most likely anyway, AND you can use it for things like Quick Sync with Virtu.