300 Wby Mag with new barrel

[svehn]

I am getting my 300 Wby rebarrelled with a 30 inch barrel. It had a 24 inch before. On the old barrel it liked 90gr of H1000 with 150gr TTSX. With this new barrel I am hoping to get a bit more speed out of the rounds. Would the longer barrel need a slower powder like 50BMG or US869 to acheive this or would the H1000 be slow enough? Any info would be great. Thanks.