Would welcome some advice on .177 target air rifle power as follows...

First question...

What is the maximum range an 8 Joule 10m target air rifle (such as a Walther LG400) can be used accurately at?

The reason I ask, is that I want to shoot either indoor 25 yard (NSRA 2510BR15-18 target) or 20 yard bench rest (NSRA 2010 BR17)

Will a modern 10m pcp 10m target rifle be accurate at the above ranges. As I can then use it for 10m, put a scope on and then shoot the above too.

Second question...

Am I right to assume that I would need a 16 Joule air rifle to shoot out to 50m?

look forward to responses.

cheers