Refer to this thread I answered, all the info you need is there.
http://www.tomshardware.com/answers/id-3746731/vbr-cbr-cqb-lossless-gamplay-recording-1080p.html
It basically comes down to YouTube's conversion bitrate for 1080 uploads being a 1/3 or less than that for 1440 uploads. It's also part of what is making 1440p displays so popular.
YouTube recommends 12,000 bitrate for 1080p uploads, but most of what makes them look crappy is the low bitrate they convert it to after you upload it.
Just capture via ShadowPlay or Relive at 50mb/s, then resize to 1440p and compress to 30Mb/s in Avidemux before uploading. It will make them look WAY sharper.
The only caveat is the upload will take longer due to being 3 times the file size, but not too bad if you have a fast ISP and short video. On my 7Mb upload speed I can usually upload a 10 minute video in under an hour.