I haven't read the New Atkins but I did read the original book and do like the authors, so I think it should be perfectly good. Some other books I have found to be helpful are The Diabetes Solution, The Paleo Solution and Slow Burn Fitness. For each new book I read, I incorporate some of the advice if it seems like it will work for me and end up with my own personalized diet.
You will get conflicting information from each person you talk to. I have tried low-fat, high-carb, restricted protein, super high fat, etc. Each time I would keep track of how I was feeling, my weight, blood pressure and blood sugar. I have had the best success with < 50g carbs, 100g of protein and the rest fat. But each person is different so you may have to just test things out a bit.
Ribeye is fattier than sirloin but I wouldn't worry too much about different cuts, just pick your favorite and if you want more fat, then you can always add it in. For example, when I have filet mignon, I will cook it in butter. But when I have my ribeye, then I let it cook in it's own fat.