Yep that kind of thing I've yet to do myself takes alot of time, debated about extentions in the past but so little room so a new PSU would be the better option due to lack of back panel space, the new seasonic idea with a slim brick behind and shorter cables seems like it will be a new thing a lot of psu makers will copy that seems like a much better option next build for me
Enjoy the weeks of sleeving