You're going to get a million different answers about helmet suggestions.
Honestly, the problem is not the helmet, it's the lack of fairing.
It's a naked sport roadster. You could add a windshield but it will ruin the look.
Although the Monster is fast, it's not the right bike for sustained high speed.
...and rider dimensions/size...and general riding posture (in conjuction with rider dimenions/size).
Pavle, unfortunately, helmets are kind of a "jack of all trades, master of none" thing, sure, all provide minimum safety for your noggin', all provide a specific airflow, all of them provide a specific aerodynamic, thing is, some of them are better than others when it comes to specific things but none of them excell in everything, for example, one helmet may have better aerodynamics compared to another one but...it may be worse when it comes to ventilation for example, or it might be be heavier, have a worse visor system etc etc...You just have to decide what you need most out of a helmet and then go for it.
For example, if you go for a pure racing helmet (say, an AGV corsa), it will (most probably) provide some good aerodynamic but the noise levels will be high (more air vents seeing as it's a racing helmet).
Also, what i mentioned in the 1st line, it also has to do with rider dimension, a helmet that may work well for one guy might not work well for another one - and i'm talking about riders using the same bike and same helmet.
In other news :
- Don't get an AGV, they're usually shite and over-priced, for the same money you'd spend on an AVERAGE K5 (with graphics) you could get an X-lite for example which are much better usually.
- I'm 1.74 and 78Kg and the Shark Spartan (which i've test-rode) worked really well for me, it was relatively quiet, had a nice, comfy but snug fit and the aeros were good plus no helmet lift-up at high speeds (compared to my Shoei XR-1100 of old), and oh, the inner sun visor is amazing as it covers up most of your face compared to other brand helmets).
- The X-lite X802 was also fantastic (for me) since it was lightweight, had good ergos and ventilation.
It's an older model though so you'd better take a look at the newer one (X-803).
Kind of expensive but you get what you pay for.
Generally speaking though, you should get one that FITS YOUR HEAD well - i can't emphasise this enough and it's the most important aspect since a loose one will shake under high speeds (and won't protect you well in case of a crash) while a very snug/tight one will make your head hurt (obviously) after some time - sure, some helmets take a couple of days to fully "mold"/adjust to your head shape but...a helmet that doesn't fit you well in the shop (i.e: pressure on the forehead or sides/temples) it sure as hell won't get better with time, what you should be looking for is one with a snug but at the same time comfortable fit.DO NOT order one online without trying it on your head first.
Aaaaand that's pretty much it, welcome and have fun with your new 797, cheers