another thing i thought of was do you really need the zoom?
Yes. What zoom does in a constant aperture lens like the 17-55 is allow you to set your camera exposure and flash output manually for the room, then use the zoom to frame while trying to maintain the same distance to the subjects you want to capture. You can also fine tune that by how you hold the flash, and in my case, the bounce attachment I use. I'm usually bending it and shaping it with my teeth if I need to widen or intensify light.
If that doesn't work I move closer or farther or if it's a drastic change, I change the exposure slightly - first by changing the shutter because it's fastest and at my finger tips, and then if necessary, bump the flash a bit up or down. I try not to mess with the ISO and aperture much and need to keep the shutter reasonably show to get the looks I want. When I'm working, this all happens very fast and I can sneak in and out and get candid shots very easily. Even if I need a second shot to adjust, I can usually bounce out before people really start to pose. I don't have any others uploaded but I'll look to see a better example. IS is indeed a MUST. At least for me. I'll see how the ISO plays, but having better ISO and lower noise is something I'll want to take advantage of if possible. It would suck to just crank it up and get what I had before, but I'll take that if it's all I can get.