I'd keep the Blizzard with it's faster SCSI option, more memory capasity and over all better quality.
However the Apollo with the 060 fasing inwards will probably allow for better cooling option (if you intend to clock it) and still have a original CPUcover on without holes in it and/or without extra high feets on the system.
When it comes to XC/MX then yes... MC runs cooler and that usualy translate into better overclocking potensial... however it's also up the the mask of the CPU. I personaly know of a XC marked 33Mhz FPU that runs stable at 66Mhz (though at a "heatsink is a must" hot) where's the MC marked 40Mhz FPU that was intended to upgrade the system crashed before reaching 50Mhz.
