Thanks for all the shared knowledge. Fascinating stuff.

I was handling the 500x100x25mm bar last night and it really does feel solid. I certainly couldn't noticeably deflect the middle without tools. Also the bar hasnt been touched for 5 years (surplus purchase for an old project) and it just happens to be exactly 1mm longer than required. I'll have the sides milled nicely and it'll be perfect.

The alu was destined for its new role.

Thanks again!