i think the best bet would be to get what I have. Just done some research and it turns out that razer was probably making mice better back years ago than they do now.
http://www.overclock.net/t/1128321/the-deathadder-megathread
best to read this thread about the 3.5g
also note this thread
https://geekhack.org/index.php?topic=56240.0
no acceleration or prediction blah blah, you will notice it, hop inot cod advanced warfare (auto acceleration) and you will be sick lol
so the sensor is: Avago ADNS S3888
googling that shows that it is flawless, meaning no jittering so a good sensor in other words.
I believe that pretty much razer's old mice are better quality, last longer as well and are really cheap now.
https://www.google.co.uk/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=razer+deathadder+3500dpi&tbm=shop
you just have to be careful, i think if you get really cheap OEM's then synapse cannot be used meaning like no software to configure your mouse, although synapse is sometimes annoying it is quite useful for changing settings.
EDIT: oh yeah, basically the new razer deathadders have updated sensors for more DPI but they haven't really changed anything else so the older versions have nice sensors, my mouse is really on point and feels great. 3500 dpi is perfect for me as well, I cba to pay like double the price for more colour changes than just blue (RGB) and 10,000dpi when 3500 is adequate for me