DPI doesnt really matter as long as it goes about 1500 or so (depending on user). I personally think razer products are crap, but lets leave that opinion aside. The best advice I can give is that you try to get your hands on these items before buying.
if i had to recommend a set without any additional information, it would be the Logitech G9x and sidewinder x4 keyboard.
See the thing about the imperator is that it looks just like the G500 ...40$ on newegg Id say nothing comes close to the mamba I just wish I had a local store that can let me sample it
I do have to say the mechanical keyboards felt good typing really nice!
Just not sure cause I can get the stealth for 140 (no discount) vs the regular blackwidow ult at 100$