We don't even need to go into Toonforce Lobo honestly.
I've yet to see any on-panel real feat for the Sentry, minus the very much disputable one-off showing with Molecule Man, that would make me believe that average Lobo wouldn't trounce practically every version of Bob.
And by average I'm talking Superman/Lobo, Reign in Hell, Brightest Day and R.E.B.E.L.S. Lobo.
And what is ripping Lobo in half supposed to accomplish anyways? He just regrows from one of the halves.
Hell, even if Bob completely destroyed Lobo's body, Lobo has become an unbodied spirit capable of possession and he would just kick Bob's astral ass.