I am assuming by "maximum impact", you are referring to maximum traffic? If that assumption is correct, then you need to analyze your particular stats to see when you usually get the most traffic. Then optimize your posting to fit into to that. Many variables, your location, target audience (local or distant), time zones etc.
If you are blogging when you have "time or inspiration" then the answer is blog when you have "time or inspiration".
Overall depends on your goals for your blog - get "mad traffic hits", optimize ad revenue etc. or blogging because you love music, want to expose new music and share. Or a combination of both. Everybody has different goals for what they want to achieve with their blog.
Never read your blog so don't know where you are coming from but that's about all I can think of. Oh yeah, Alyssa has a good point about the RSS feed thing.
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