Sell the 75-300 and pick up a 50 1.8/1.4 I strongly recommend 1.4 mainly due to build quality and hard edges for 1.4 (vs 1.2 IMO is soft and it cost 4x the 1.4) or sell both and buy 17-55 2.8 used ones like 875 on eBay
cause 50 is nice but u will hate life sometimes u want to be closer to the subject and still get wide shots. So that's why I said sell only 75-300 unless you sell both for 17-55 2.8