The question for yourself might be, why you want to use cdj’s? Is it the name pioneer, it’s what all the big guys using, they take me more serious.
Next question what do you like to do with it.
What kind of dj you wanna be?.
Do you want to start dj’ing without traktor if so go for the 850’s but better the 900’s if you want to use a hard drive. It’s a hassle to keep two drive’s synchronized. I now, i got two denon 3700’s and ended up for this reason using midi. And then it’s a lot of cash to throw down for all the extra you pay like usb and cd and not use it. Then the 3700’s have at least spinning platters.
You say you like to use traktor, Traktor s4 is an optimized controller for the new software.
The jogwheels seem to have a same feeling as the lower end pioneer cdj’s
At the end, i think you have more fun with the s4, and after the update for timecode control, you can always buy some cdj’s and connect them.
The only thing, the s4 is not a analog mixer so you always be stuck with a laptop. But if you keep your laptop just for dj’ing as i do, you won’t have many problems with a controller. in the 3 years and playing twice almost every weekend with my denon hc4500 i never had a real big crash.
You probably can buy the s4 and a decent laptop (maybe even a macbook pro) for the price of two 850’s and a mixer and you probably want something like the kontrol x1.
Really first get a honest answer why you want cdj’s.
After that what ever you decide it’s your decision and those are the best.
Enjoy the process, it’s always nice to buy new kit.
Thomas