I shoot a D3200, I use, what were when I got it 'fast' 45Mb/s SD cars, but as others have said, that's only the nominal rating of transfer speed, and usually brought 'up' a lot, particularly on cheaper cards by a faster read speed, and a slower write.
HOWEVER.. why on earth do you 'need' to shoot in NEF + Jpg?.. why are you trying to 'machine gun? Why are you BASICALLY overwhelming the poor camera?
RAW.. is a raw nerve to me.. a bit like 'Pro's go Manual (exposure!)' .... its a peculiarly 'amateur' attitude... pro's use as MUCH 'automation' as they can.. they don't want to be wasting time 'faffing' with stuff when time is money... and the money is what makes them a pro, ot how good thier pctures may be! Its an indulgence of the amateur/hobbiest who can afford the time to 'faff' and when it doesn't really make their photo's any better for it, they resort to the retort that 'they' are taking control... NO.. most often they are just FAFFING for the sake of, and making a big deal of the business for the sake of! [Rant possibly over]
RAW... isn't, for starters... there is a presumption that the RAW format files record the actual 'base' light levels off the sensors receptors.. which they don't.. the sensor array is made up of filtered receptors for Red, Green and Blue the camera's electrckery interrogates the sensors, gets readings then interpolates those readings to create artificial 'pixel' values for a photo-file....what RAW formats usually do, is record an 'extended data set' that 'may' include some of the lower-level almost base data, 'close' to the sensor readings, but also the algorithms used to create the picture-set, so that it 'may' be back-tracked in adjustment... which is all probably a bit Geek-Greek to you, but don't worry...
NEF, as in Nkons 'pseudo' RAW file format, I dont know exactly, but NEF probably stands for Nikon, Editing Format, or Nikon Extended (jpg) Format .. therein lies the hint of the 'redundancy' duel-saving in NEF+JPG... Nef already IS a JPG format image file.. it merely contains a second data-set that explains how that Jpg was created, to allow more or alternative processing to viewable image file to be made by the user.... it may be a handy feature if you want 'quick' Jpg's to show and share, but the NEF's to play with at leisure, BUT for the most part it IS just a great way to clog your cameras electrikery..
Next up... I do NOT habitally shoot in RAW... I see no need..... I did NOT spend umpety hundreds of quid on a fancy all singling all dancing automated photo-bot to turn all that electrickery 'OFF' and try shooting it like my old Clockwork Film Camera, and then spending more ruddy time than I did n a dark-room developing and printing, faffing about in View NX messing with sliders, to do something the camera should have done for me... and if it DON'T then probably because I effed up before I pressed the shutter, and no amount of turd-polishing will 'fix' what I got wrong to start with!
For YOU as a beginner... NEF / RAW is probably NOT helpful; you do NOT 'make' photos in post process, you make them in-camera, and f you haven't got it right in-front of the lens before you press the shutter, you are onto a looser trying to sort it out after.... and its a road to madness even trying, and worse beveling that you should!!!! Get it 'Clean-In-Camera' get it right first time, at point of capture and you NO NEED to post process at all; THEN for all the small added flexibility you have from a RAW or Extended file to change the way the image is converted from numbers to pixels you can see, matters little! RAW/NEF really has very limited scope to change stuff, mostly the base exposure and contrast; you CANNOT correct out-of-focus you cannot correct Depth of Focus, you cannot correct motion blur, you HAVE to get that sort of stuff 'right' right at the start.... post-process faffng and shorting in RAW/NEF you HAVE to faff with even to turn into a view able display format file, like a Jpg, is leading you down the garden path AWAY from getting it CinC, making you believe you 'can' correct 'anything' in post.. you can not! So don't even try!
Advice therefore IS... Shoot JPG 'only'.. work on getting your shots Clean-In-Camera, put the effort and attention in upfront at point of capture get it right first time, let 'duffers' in the Jpgs show you where you effed up! Don't wast time turd polishing, spend it instead trying to work out what you did wrong and putting it right for ext time, 'upfront' for CinC.!!! Your SD card will love you for it!
Follow on from that is why machine gun? Slow down TAKE your time, pay attention, get it right in camera, don't presume to spray and pray, that 'something' in the stream will have turned out 'OK'.... As Phil pointed out a film camera that could, with a motor-wind shoot at more than two-frames a second was going pretty good..... and STILL folk told us with wonder-winder equipped auto-fantastic cameras to SLOW DOWN, pay attention,... You only need take ONE photo... IF you do it right! And THAT is where the art lies! Truth in that bit of base ludditsm has't changed just cos electrckery has made cameras quicker and packed in more features!
This would to my sense of sensibilities be a pretty typical case of modern techno-marketing over-loading your plate with too much technology for newbies to get to grips with, and make a whole plathora of alternative 'mistakes' to when we used to have to twiddle a focus ring, and only had two or three things we could have possibly effed up!
Basically your SD card is telling you you are trying to make the camera do too much, because you are doing too little, and are trying to cover all the bets on the table.... back off, slow down, get strategic, get savvy, learn what does and doesn't really matter, and believe me, MOST of that is infront of the camera, NOT 'in' the camera, less in the settings, menus and options!