If you've been skating on Jacksons with no issues, then go with the Premiers. Changing boot brand and blade both at the same time is asking for trouble. Especially considering a move to a totally different boot design with a totally different heel lift, like Edea.
For a synchro blade, Coronation Ace would probably be a decent option. You probably don't want MK Pro for synchro, because the tail is very long. Another "intermediate" option would be the Ultima Finesse.
But if you've been skating on those aspires for a long time, then it's probably better to bite the bullet, stay with the 8' rocker that you have on those XPs, and go straight to a higher end blade.
MK Dynasty is a great option that is specifically designed for synchro (it's basically a Pattern 99 with slightly shorter tail and different stanchions apparently better suited for synchro).
Paramount Synchro despite advertised as "comparable to MK Pro", is actually 8' rocker I believe, and so closer to the profile of a Gold Seal, just with shorter tail and different stanchions.
From the two, Dynasty is going to be closer to your Aspires with a flatter spin rocker. More advanced synchro teams might also have some requirements as to what blade they want skaters to be on, so the Dynasty is probably going to serve you better in the long run in that regard as well.