Don't you already have an Ampeg 4x10 HLF? If it is made by SLM I would keep it and find and amp that sounds good with it (An American made Ampeg SVT 3 Pro for example), if it is made by LOUD trade it for the Orange. But then you have to worry about trying to find an amp that sounds good with the orange cab (maybe the LMII). Dude, seriously, you need to decide what sound you hear in your head and try out different gear until you are able to say "this is it!" Once you find it you will know. Asking people what they think is better does have advantages, they have different amounts of experience, but everyone has different opinions, you are never going to find a rig that everyone will be happy with ... but if you are that is all that matters. Just my $0.02. Cheers.
If you do decide to go with a 3 Pro, rewire your cab to be 4 Ohm, your head will then pump 450 Watts RMS instead of 275 or something, lots of people complain about the lack of power from the 3 Pro I think it is just because they aren't using it at 4 Ohms. Cheers.
Just checked it out and yes you are right, I don't know what I was thinking ... The 4x10 HLF is infact already 4 Ohms. Sorry to have worried you. Cheers.