Mike
While I got all my extrusion cut to size from KJN in the UK, I do regularly cut extrusions up to 45x90mm. I've always used a standard Delta brand 254mm (10") sliding chopsaw with an aluminium cutting blade - the type they use for aluminium window and door frames. It is set up accurately for timber and I just swap out the blades (if I can be bothered, it works with an ordinary 80T woodworking blade !) - it makes for a very clean cut - especially if you spray paraffin (or water even) from a spray bottle. I make sure that the extrusion is always mechanically clamped at both sides of the cut and take it at a slow even speed for a nice quality cut. You CAN hold it by hand, but if it bites, you end up with a bad cut (and perhaps four fingers
)
A colleague has a 'metal cutting' chopsaw, but it has an abrasive disc in it and just makes a mess of aluminium - not too bad for steel. He also has a steel bandsaw/hacksaw, but it is nowhere near as good as my chopsaw.
Cheers
Neil