I didn't listen to the song... but I will share with you my thoughts...

Tempo can mean different things to different songwriters because lets face it... some songwriters aren't classically trained in music theory. Tempo... to those that are classically trained would be the beats per minute... time kept by a drummer in most cases... For me... someone who likes to ignore most cases of musical theory and hit the artistic side of music right in the gut... tempo is simply the pace of a song... in which can be kept by a guitar, drummer, bass... or whatever... I see what you are saying by speeding up a song and making it sound like it's in fast motion... What I usually do when I change tempo of songs for added emotional value or to add a certain exclamation to a part of a song is I double time it... take a riff and instead of playing the same riff note for note... and double notes in and make it sound twice as fast but over the same beat... or you can double time the beat as well. This allows you to speed up and slow down without losing the dimensions of the song... As for parts that you're going to sing over... that's a different story. Trying to speed up a song and keeping the same melody would obviously make it sound like it's in fast motion. My suggestion for this is to work on a different melody for the fast parts... something that can tie in with the other melody... this way the music can speed up in the background and you can stay within the song lyrically without sending it into Alvin and the Chipmunks mode. This is very useful when trying to add a certain amount of emotion to a song... like a sense of desperation, urgency, fear, or excitement... to name a few... Try to come up with a melody that can go over the sped up pace without going outside the song lyrically and I think you and your drummer can work this out. I like the idea of speeding songs up and down... it gives your music depth and it keeps the listeners on edge. Good luck!