The strong G's on Manta are from that pretzel loop,which at least for me is one of the most intense maneuvers on any coaster,your description states my point that different people can tolerate different things whereas one person might ride a coaster and not bother them at all,someone else will have a totally different reaction.For example I do agree that RnRc does give me a bit of neck banging even though it's not a major coaster.On the other hand Kraken,Mummy,and even some of the biggest coasters on the planet like Millenium Force at Cedar Point I would ride all day long if I could,in fact I think one time near closing I rode Kraken like 15 times in the last hour of operation.Manta is a pretty enjoyable ride except for that pretzel loop,I think the most I could do that ride in one day would be like 2 times,only because of those 3 seconds when the ride does the pretzel loop,I know other people feel it as well but I think that sensation might bother me more than others,I can handle 300 foot drops at 90 mph but Manta's loop REALLY bothers me.