I like this new addition that makes guardians unique, however, it feels pretty counter intuitive. From the quest, you get a 310 artifact and those two that you choose from are the only ones that can get that high. If you infuse even a 300 one with that it will only be 306-308 probably. I don't think there's a way to get artifacts of your choice to 310. :( Edit: The only way I can think of to get another artifact to 310 is to transfer a 310 artifact from a character that has also done the particular quest to obtain the artifact and infuse it to 310.