mettelus
It sounds as if you are already deep into the project with a lot of tracks. Based on that I would tend to finish it "as is" and then adjust the final mix down track. Audacity is a free program that will do this fairly well, and if adjusting by only a few percent should not be egregious with artifacts.

It's one of those songs where the verse actually feels a little better right where it is, but the chorus feels better and more appropriate a little faster, for the planned vocals.  It's almost a mood thing.  The rest of the tune could work as it is too.
 
My plan is go ahead and lay some test vocals.  Along with re-recording an acoustic track with the tempo up a little bit, do some test vocals on that too and then compare the two.  
 
I'm telling you, the guitars are not difficult or anything, but damn I really got them tuned up well and the acoustics and electrics just sing together during the chorus part - turned out exactly how it sounded in my head, which is rare.  Just hate effin with that, ya know?  
 
I have audacity too, so I'll test that tonight.  I'll admit, I have no confidence in it, but it's worth a test.  Thanks! 

Audacity is an insanely good/useful program for what it is. It does certain things that most top shelf DAWs don't and you gotta pay through the nose for to get elsewhere.
 
Of course it's limitations make it kind of useless as daily use DAW (like no real time FX tweaking) but some of the included tools/features are pretty surprising... and that's completely ignore the fact it's free.
 
I recently found out it does hardcore wave editing stuff that I've been eyeballing other programs for that costs hundreds of dollars. I still "need" those other programs but just knowing I can get all wave mangly with Audacity is pretty cool.

What I would do:
Export the mixed project (sans vox) as audio.
Import it into a new SONAR project, select the track, go to Process>Length and set it to 95% or so.
Then record your vox.

Beepster
Audacity is an insanely good/useful program for what it is. It does certain things that most top shelf DAWs don't and you gotta pay through the nose for to get elsewhere.
 
Of course it's limitations make it kind of useless as daily use DAW (like no real time FX tweaking) but some of the included tools/features are pretty surprising... and that's completely ignore the fact it's free.
 
I recently found out it does hardcore wave editing stuff that I've been eyeballing other programs for that costs hundreds of dollars. I still "need" those other programs but just knowing I can get all wave mangly with Audacity is pretty cool.

There's a whole suites of plugins for Audacity and it can also load some VST 2.4 plugins.
http://audacityteam.org/download/plugins