Pretty sure pushing the power section of the Orange would sound rubbish. There is a limiter in it, which the 4/8ohm switch alters, so it won't break up as such, just limit, which might also be ugly.
I certainly wouldn't want to push the power section into limiting - don't want ugly. I suspect the gain structures might behave differently between the Gallien-Krueger and Orange amps so the comparison might not be apples to apples. I see more metal, thrash and other high volume players using the TB1000 with classic rock, blues, and funk players favoring the TB500.
The TB500 can peak to 900w; I don't even want to know what the TB1000's peaks would be. That said, depending on the efficiency of those cabs, you might be able to run the 1000 more conservatively and have a bit more clean headroom without actually exceeding your drivers' limits. I do know a local bassist who runs the TB1000 with nothing but an Epi 3x10 rated for 700w and he hasn't had any problems with blown drivers.
If preamp gain is used for your saturation and color while amp size just provides the headroom you need without altering the sound much, then the 500 vs 1000 choice might just be a matter of how much headroom you need? The cabs I listed are quite efficient and if the TB500H can drive a steady 500 watts with peaks up to 900 it looks like a more than adequate match. Thanks.

