Go back to Pro Photo and get a D700.
I've very recently been shooting pretty much exactly what you've described you'll be doing, and i'd hate to be doing it on a D300.
For example, here's a portrait i shot at ISO 3200 and f/2.8 on the 50mm f/1.4G:
and it's pretty damn clean. Not to mention, the D700 at the high ISO's keeps quite a bit of dynamic range. So the combination of low noise, and high DR, means you can post-process into oblivion.
For sports, you need reach and high ISO. Sacrifice the reach, take the high ISO. when i shoot triathlons, i'll just keep the camera at ISO 1600 by default. The pictures never get printed bigger than 8x10, and at 1600 you can barely see noise on an 8x10, if it's matte paper, you can't see the grain. As far as FPS, the D700 if you're in single shot, will go 8fps without the grip if your finger is fast enough...in 14 bit RAW. how fast is the D300 in 14 bit raw? 1.5 fps or something like that?
Weddings are the same. Imagine shooting receptions, rent a 24mm f/1.4, and you've got night vision in color.
Even though the D700 is the oldest camera in Nikon's current line up, it's damn near perfect for sports/event/location portrait if you don't need video.