The 378 GNR is based on the 405 Win. case, whereas the 375 JDJ is based on the 444 Marlin case. If you are strictly looking for power the 378 GNR is stronger than the 375 JDJ. The 375/06 JDJ is more similar in power. The 475 JDJ and the 475 GNR are the exact same round they just go by different names, just like the 416/348 JDJ and the 416 GNR. It is hard to go wrong w/ any of JDJ's rounds or any of the GNR's. I would look at the level of power you want and things like the case costs and availability. If you really want power go w/ the 476 GNR which is based on the 50 Alaskan case. This round is very similar to the 470 Turnbull.