Here is a mashup I finished working on a few days ago.I tried everything I could think of to get rid of the drums in the second verse of the Save Me acapella,but no luck... link
I'm really sorry, but I don't think they belong together. I couldn't listen to more than 10 seconds. No comment on your technical mixing ability, I'm sure you can do great mixes, this just isn't going to be one of them no matter how hard anyone tries.
I tried a Save Me / It's a Hard Life one once, and it almost worked, but only because I switched back and forth between the two, and only occasionally overlapped them. I ended up throwing it away in the end because it just didn't gel.
So, I hope I'm not scaring you away from remixing, again, I'm sure you can do good stuff, but the concept itself (Save Me overlapping Spread Your Wings) probably won't work, as intriguing as it seems.