If you print these items in the orientation shown (45 degrees) with support selected, the post printing clean-up is much easier, and the 100mm straight is printed in less than 1 hour, in the upright orientation it takes over 2 hours. As you can see the support printed is only 2 layers deep, and also acts as a brim, helping to keep the part stuck to the bed.

The only problem I can see is ensuring that the straight stays stuck to the bed (doesn't warp), which can be helped by increasing the bed temp about 10 degrees above normal.

Earlier today I printed a 230mm long straight (sorry no picture, yet!), using the "scale to size" option in Slic3r Prusa Edition. It took just under 2 hours to print. The longest straight you could print on the Prusa Mk3 in upright orientation is 210mm, and would take about 4 hrs 45mins.

Prusa

i3 MK3

No

Yes

0.2mm

20%