Hi Lefty
The combo weighs 70lbs - its a bit more than some of the opposition which seem to come in around 50lbs - but because its sort of a taller, narrow shape it seems quite easy to grab and lift if you know what i mean. I was initially a bit sceptical about the weight when i bought it, but in reality it hasnt been an issue. It has 2 good high, side mounted steel handles.
Re the contour controls - they both act as a scoop but with different parameters (prefer number 2 myself as it seems to give more of a rumble).You can also have them both switched out obviously for a middier tone. Im not familiar with the 450 for a direct comparison i'm afraid.
It has loads of headroom. Ive never needed to have it above 3 in a rehearsal room with 2 guitarists and a loud drummer and there is no distortion or fartyness occuring even when you crank the bass up. The 15 definitely gives a bigger, warmer rounder sound than 10's for sure. It seems to be from the "set everything to zero then tweak a little bit" school. The TweeterTone makes quite a subtle difference to the tone as well as adjusting the tweeter level - it appears to round the sound a little as its reduced.
Its a fantastic amp for the money and should see you through most gigs.
Heres a link to the user manual
http://www.tcelectronic.com/media/BG500_us.pdf
and some blurb from TC with a few interesting video demos here
http://www.tcelectronic.com/bg500.asp
Cheers for the interest