T8x2 Config Speed/Accel setting is too aggressive

[Poofjunior]

The settings for T8x2 leadscrews in the config somehow managed to get lost in the config on a later update. T8x2 cannot go as fast as the T8x4 ones.

For T8x4 Screws, we should have:

M203 X18000 Y18000 Z1600 E8000 U9000    ; Maximum axis speeds (mm/min)

But for T8x2 Screws, we need to go slower so as not to stall out the motors with skipped commutation steps

M203 X18000 Y18000 Z800 E8000 U9000

In practice, we may be able to go a bit faster than 800mm/min, but we'll need to thoroughly test whatever value we want to increase it to.