The impact of your EPQ on your application will depend on the universities and course you are hoping to apply for. Some universities will lower your offer by one grade providing you achieve an A in your EPQ (although some universities only ask for a B in order to get the lower offer and I knew someone who only needed a C to have theirs lowered!). Even if your first choice university doesn't lower grades for EPQ they're great to demonstrate wider reading/enthusiasm for your course and they could be a good discussion point for potential interviews. I ended up applying for a course that wasn't relevant to my EPQ and universities still lowered my offers, so it's not the be-all and end-all to choose a relevant topic, people end up changing their minds about courses all through sixth form anyway! Instead, I explained on my application how the process had helped to improve my research and analytical skills. It's best to have a look at any universities and courses you're interested in and see what they say about EPQ so you can get an idea.