After looking it over again..seems like you are getting a lot more with AC/DC prem vs Met Prem. I think this is more of a good thing with the pro metallica have more stuff than a pro AC/DC but interesting none the less.

MET
Moving Grave Marker
Hammer Ball Lock with Disappearing Magnet, coffin lock
Moving Snake Mouth
Color Changing LED's GI/inserts
Metal apron
Slide rails, lockdown bar etc....
Spaker Grill inserts

AC/DC
Lower Playfield
Bell
Moving TNT detainator
2 sets of drop targets with standup behind TNT
Train
Moving Band Members(admitedly kinda lame)
Powder Coating
Flashers in Apron
Color Changing LED's GI/inserts
Diverter ramp

10 differences vs 7
Toys wise I say
Hammer Ball Lock = Lower Playfield
Moving Grave Marker = TNT
Talking Snake = Bell

So with AC/DC you get
Drop Targets, Diverter and some more bling

I was just being lazy

Also I am not comparing AC/DC to Metallica...more the difference in Pro vs Premium on the two games...seems like you get a lot less in AC/DC pro..or more in premium depeding how you want to look at it..thats my point

I think overall Metallica seems to have more and cooler toys! Just so happens two of the good ones, Sparky and the inline drops are on the pro. So this may be more a case of Metallica being a better pro thats all.