Don't you just love it when people just offer their opinions totally ignoring the original question?
OP asked which card to get out of two choices, let's take your line of thought that the 5750 is spectacular, best GPU that will ever be created. We are going to take that line of logic and apply it to your strengths for the card-
1) Power Consumption- The top card will be better due to lower clocks
2) Noise- Bottom card will take the nod
3) DX11- What attribute? Performance wise, bottom card
4) Smaller Card Design- Top card is smaller due to the shorter HS/F, both are dual slot
5) Eyefinity- Bottom card will be better due to higher clocks
These features could easily tip the balance to a 5750 over a 4870 depending on the individual.
Which may explain why the first response to the poster was asking for clarification as to why he wanted a 5750. As a generic question, any of them are poor choices. If the OP did have one of the particular concerns you brought up, it would depend on which one was more important to him which of those particular 5750s would be better suited for him. Perhaps the people who frequent the vid card forums are very well versed in all the differences between the available options and due to this we post the best option given the available information along with asking questions that may change those options.
The OP did not offer any qualifier as to why he wanted a 5750, without a particular need it would be rather shameful for the people on this forum to reccomend one to him when we are all well aware of the fact that there are better and cheaper solutions available for most users needs.