I've never had much use for 2400, but I've burned probably about a ton of Unique. Hard to beat in a great many calibers, but I did note some forcing cone issues with heavy loads in .44 magnum. OTOH, the forcing cone wasn't properly done in the first place and after cutting a proper cone, didn't note any further issues. There are, of course, better powders for stout loads, especially in .44.

I will admit I don't go for the max loads anymore, regardless of powder selection. I didn't notice any significant difference in terminal performance between a 125 gr JHP (.357) at 1250 f/s and 1450 f/s. The latter is obviously harder on the gun.

I do recall warnings about the use of Blue Dot in low temperatures possibly causing over pressure events. No memory beyond that as it was never a powder I personally used.