When I had my 4.6, I didn't use it at lower speeds but at 80 it held steady, rarely used it though, wasn't very often I had traffic
conditions to maintain a reasonable cruising speed.
I remember "back inthe day" we never used torque wrenches on wheel nuts, just an extra "nip" on each nut, in all my years of
driving and working on motors, I have Never had a wheel nut work loose but, I torque em now so, they are not overtightened.
I'm the opposite, which is why I usually torque smaller bolts, to prevent shearing them, all too easy to shear a 10mm bolt with
a 1/2 drive ratchet, I don't torque drain plugs though, just a nip, so I can undo it next time.;)
I've thought of an easy way to check this, fold a piece of cardboard, an empty cereal box would do, so it stands an extra 50mm
on top of the existing battery and, close the bonnet, if it doesn't crush it, then the MF31 1000 should fit.