Actually 5w50 taglon is not mineral based it is fully synthetic oils and one good reason to choose a fully synthetic oil that it is less thicker and better than mineral oil based oil.
And 2ZRFE engine of grande is filled with 20w50 from factory because thicker oil helps in engine running.
Now the problem with 10w30 or 5w30 is which i have been using in my grande is , if you are operatih you car under extreme loads the oil do not stand lot of miles. It gets black and the performance also decreases (i tend to drive on high rpms 5-6 and do hard acceleration and drive on higher speeds 160-200 on motorway). 5w30 or 10w30 is good for fuel economy but bad if you drive on high rpms
So because of that i have shifted to 5w40 fully synthetic. And i guess this is the problem thats why imc is suggesting 5w50 taglon for grande.
Someone here also mentioned that this ZR engine have problem of maintaining oil pressure at high rpms so use high grade oil like 5w50 or 10w60.
Because me and my friend @haseeb.basharat have had not very good experience with 10w30 in this engine he is shifiting to 5w50 and me to 5w40.
After shifting to 5w40 i have experienced lot of improvemtnt in engine performance plus noise of engine has reduced significantly.
Remember fully synthetic oil are less thicker than mineral based oils. So using 5w50 taglon which is fully synthetic will not harm ur vehicle but will be great.
So first oil change is at 5k kms. But i did my first oil change at 2k kms.