I run Win 7 in a bootcamp partition on a 5 year old MBP and am running 10.9 on the same machine. Here are my observations:
1. All Microsoft apps load in about half the time it takes similar apps on 10.9. It's not even close. I am running the latest versions of the entire MS suite on both systems. The hysterical thing is that I believe the fastest windows laptop machines available are Apple Macs running windows in a bootcamp partition. I've seen this on new MBP's at work. There is definitely some irony there...
And one other thing they have in common is a 'Screen of Death'...Windows of course has the Blue Screen of Death, or BSOD and now OSX 10.9 system lockups are the equivalent. Way to go, Apple....
2. With all that said, Win 7 is remarkably stable, I run Autocad plus several Windows-only apps like Visio, MS Project and it just flat out works well. It took MS 20 years to get there but they did it...and then they phoqued it up with Win 8, which is very stable and faster than 7 but the UI is all FU'd. 2 steps forward and 2 steps back.... (the Win 8 references are based on a winTel PC I use at work).
3. Boot up time on my MBP, windows 7, hands down faster to boot and by more than a few seconds.
4. Shutdown time is not as fast on Win 7. I tweaked the setting on 10.9 per some thread on this board so it shuts down VERY fast now.
So performance wise, Win 7 is a hands down performance winner all things being relatively equal on my MBP BUT from a UI perspective, well, I'm still a OSX kinda guy.
Open a 3rd party app on both of them. You can't compare opening MS apps on Windows and OS X. MS apps on Windows use frameworks that are already in memory when you boot into Windows. So when you launch them there's less to be copied to memory. It's not the case with OS X obviously. Open Adobe Photoshop on both of them for example and test that.