hello. dealt with many backing issues. there are pro's & cons to be looked at for sure.
if you are setting up for salmon/steel i would definatly go with 30lb. only one reason why you might not, that being reel capacity. depending on where you plan on fishing i realy don't believe you would ever need over 200 yds. i would feel comfortable with 150 even on larger waterways. for smaller tribs 100 yds is plenty. the heavyer breaking strength is handy to have when fish are crashing in & through wood. SG