Yea thats the one.
G9 = Wireless G5, yes?
No. that's the G7. G9 is wired and has a new design. It's geared towards "finger" users. G5 is tailored to palm users.
I use G5 and i'm absolutely happy with it.
I haven't heard much about the boomslang series but if I was to choose between Razor and Microsoft Razor Wins.
My last Microsoft mouse was the IntelliMouse Explorer 3.0. It was marketed to have best egronomic design for its time and I got hand cramps after using it for 3 years or so. So far, nothing yet from my Logitech G5.
I haven't actually used a razor mouse so I can't say but Logitech makes pretty nice mice too. It depends what you need really. If you need the extra profiles Razor does it a lot better.
Design wise Logitech and Razor comes pretty much head to head.