Erm... Sky Shadow was responding to your comment, "universe is more accurate but a different mold" -- and Universe Starscream is just a repaint of the same mould as Classics Starscream, whereas Masterpiece Starscream is a different mould and sold in the same "Classics" style packaging as you can see here. You may have meant to say a "different redeco of that mould", but your actual wording was "a different mould," so I can understand how Sky Shadow came to the conclusion that you may have meant Hasbro's Masterpiece Starscream.
Alright, the following Classicsverse Seekers were released in Australian retail:
+ Classics Starscream
+ Classics Skywarp
+ Classics Ramjet (I know you don't want him, but just mentioning)
+ Universe Starscream (repaint of Classics Starscream)
+ Universe Acid Storm
+ Universe Dirge (repaint of Voyager Cybertron Starscream)
+ Generations Thrust
+ Generations Dirge
+ Generations Thundercracker (which you already have)
Other than Thundercracker and Ramjet, which two should you get? I don't know... depends on which ones you like. It's entirely up to you. But those are the ones that were released in Australian retail, so hopefully you can find them domestically.
Well yeah, he is being powered by the Underbase!SCF/HOC Omega Supreme would be close to scale to MP Starscream to recreate that particular moment.
Meh, I prefer the Takara reissues -- at least they kept the original names (cos Hasbro no longer have the rights to the names Bombshell and Shrapnel). The Takara reissues also came with 3 Energon cubes... I don't think the Hasbro ones did. Neither set were released in Australian retail, so either way you're gonna have to import if you want them (though the Hasbro one is more recent, so may be easier/cheaper to obtain on the secondary aftermarket I guess).