As above regarding upload speed, but you can make some real savings on file size with a good video editing program. Remember that YouTube is going to convert your video to to a H264/MP4 format whether it's SD, 480P, 720P, 1080P or if you're lucky enough to own and use a 4K camera 4096x3072 pixels.
For instance a 720P video on YouTube has a bitrate around 2-2.9Mbps. A 1080P video is 3-4.3Mbps. It has to be this size so most peoples internet download speed can cope with it.
Have a look at this for an example. This is a short 1080P video I shot at the 2010 British GP. Only 23 seconds long but in it's native format it's 127.6MB.
Here it is in the timeline:
And when it comes to the output stage you can see that by saving it as a 1080P WMV at 8Mbps the end video is going to be 23MB. That's quite a saving before you upload to YouTube.
Say you encode as a H264 MP4 at 4.3Mbps (the maximum bitrate YouTube uses):
Well that's only 12MB. A saving of 115MB.
I've done this using Premiere CS5.5, but you should be able to get the same results with any good video editing software. I haven't used the Vegas family, but I would bet that the version starting at £80 will do all you want.
http://www.sonycreativesoftware.com/vegassoftware