Well its generally excepted that them five are the best performers, there are others out there but they are normally little more expensive or harder to come by ie Supersprint/Sebring/Ashley/Jetix/Remus/Devil
Personally I would have been more drawn towards either another Peco or Sportex back box as Im not overally sure if the the value of say a new Magnex/Janspeed/Piper/Mongoose/Scorpion would be worth it on a 1.1 but like I mentioned it would be a different story if you could sourch a secondhand unit.
It might be worth looking to non saxo back boxes also as the acutal cans are pretty much the same its just the pipework that comes out the other side that links the can to the rest of the system that changes.
A desent custom exhaust shop or mechanic could weld new pipework on the end of the back box and new hangers as well for you.
Not to everybodies tastes but custom is alwasy another option look to eBay or
www.essexracing.com for custom back boxes.
Custom doesnt mean 5' Jap cans sticking out everywhere.
I had a custom exhaust built to look like a 2' Group N style race system and doesnt look custom.
and one from underneath
There are loads of options for exhaust it just depends on if you can find what you want and then find somebody to do it for you