From what I can see, the Acer 5810TG (click here) has a significantly superior CPU, slightly better graphics & networking, plus inbuilt Bluetooth & webcam. What I cannot figure out is why it's £325 dearer than the other Acer you linked to.
The Medion P8610's (click here) main advantages are the larger screen (almost 3" larger), Blu-Ray reader, much better graphics & slightly better CPU. Another not worth the £780 asking price at present IMO, but still better value than the Acer 5810TG.
I guess, in the end, it all comes down to what you'll be using the laptop for, & your specific needs - do you require an expensive Blu-Ray reader for instance? Do you need a gaming-grade graphics card? G