I only have a mass air system and haven't done any research related to speed density systems. I've read stuff like you have that pretty much say that they are less adaptive to major modifications. If that's the case, maybe it's true about bumping up the fuel pressure. I can't really give you answer any more than that. Sorry.
Upgrading to mass air would probably be a good idea, though.
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351W 89 Mustang GT Convertible