I honestly have no idea what you are talking about. First of all if it had issues with "scalibilty" that would mean that they were able to get a large OC but the performance didn't increase in line with OC amount but that's not what is going on in the article. The only thing that article shows is that they had a hard time getting a good OC in the core. They OCed the core 5% and the memory 19% and saw performance increase 8% overall. What is this "inherent limitation" of design that you are blaming on the memory? What does "drops in performance from OCing the gddr5 too much when the core could be pushed further" mean? They didn't stop OCing the core when it could be pushed further, they OCed it as much as they could. They didn't OC the memory too much, they OCed it as much as they could. The only thing that article shows is that the particular card they tested had a core that didn't OC well, that's it. I don't know where this other stuff you are talking about comes from.
Here is another article about OCing the card and they managed to get a 13% OC on the core and 21% on the memory;
http://www.overclockersclub.com/reviews/sapphire_hd5770_hd5750/6.htm
and another with a similar OC;
http://www.hardocp.com/article/2009/10/12/amd_ati_radeon_hd_5770_5750_review/7
and one more with a good core OC but they couldn't OC the memory as much as others;
http://www.neoseeker.com/Articles/Hardware/Reviews/hd5750hd5770/3.html
So anyway the card has no issues with overclocking and that the memory OCs even more than the core is a GOOD thing as the memory bandwidth is a lil weak for a GPU of that caliber. I think you were basing way too much on one article and then started coming up with weird theories to explain their results.