The inbred was the original xc machine, check which model (age) you get as they went from 80mm to 100mm to 120mm specced as the trend for bigger forks continued - Brant (probably) or a post on here will tell you which is which due to chainstays and seatstays.
That said I had a 100mm specced version with a 125mm phaon on it and did some jumps and general xc with no bother (at ~16 stone).
The 456 was originally designed when the inbred was being built with 100mm forks in mind - A long travel hardtail that had a some larger diameter pipes so weighed more but was able for much tougher stuff and aimed to use 100 to 150mm forks (4" = 100, 5"=125 and 6" =150mm), hence the name.
The scandal was a lighter version of the inbred for racing.
Summer season was a cheap frame for short forks being used on v steep ups and downs.
the 567 was designed for mental long forks - 2 built I think?
The benefit of steel is that you can crash it and then get a fella in a shed to weld it back together/bend it back in place - unlike the aluminium which needs a specialist to weld it and once bent is buggered.
I had a inbred and then got a 456, the inbred is lighter and the shorter fork was great for all day xc, the 456 is much heavier due to the build (alfine etc) and I'm overbiked truth be told, but it has that indestructable feeling as I'm flying over stuff, that the inbred would have been sketchy on, vice versa it's needs some oomph to get it going..
Edit to say - all the on-one's pass the CEN testing for strength, so that's not a bother. The tubes on a aluminium frame hate side hits (frame landing sideways say) compared to a steel frame - but hit anything and it'll crumple.