New router with better wireless range

[magicroundabout]

Can anyone recommend to myself a new router to replace my dir-615 so I can connect it to my 50mb broadband which gives me a wider wireless signal please.

I've no idea which is best so any help appreciated

 

[magicroundabout]

I've been looking at the Dlink dir-815 (£48) or the Dlink dir-855 (£138). But unsure why the 855 is such a premium over the 815