I would simply extend the table, with each +10 increasing the dice. The progression would be determined as follows:
nD6
nD8
nD10
nD12
2nD6
and repeat, where n starts with 1. (I forget where this matches up with the current table.)
Another possibility I considered was to have each +20 increase the dice instead of each +10. I'm thinking that STR+SIZ scores above 100 should be rare enough that it does not make a lot of difference, but it makes sense if scores up to 50 increase the damage modifier for each +5, and scores 51-100 increase the damage modifier for each +10, then scores 101-200 increase the damage modifier for each +20.
On the other hand, my theory is that STR and SIZ scores should be logarithmic, so if you're facing someone who's STR + SIZ is 241, that guy is TOUGH. :shock:
Still, perhaps for 101+, each +20 increases the damage modifier, whether STR + SIZ is 101 or 1101. (STR + SIZ of 1101 means this guy really should be able to smash up a planet. You do NOT want to take a direct hit from a guy like that.)
Another rule I've added is that instead of having Martial Arts do 1D6 damage, regardless of score, instead a character with the Martial Arts Strike advanced skill can add 1/5 his skill % to his STR + SIZ to determine his damage modifier unarmed or with a martial arts weapon. (Note, this is added to STR + SIZ to determine the damage modifier, NOT to the damage modifier itself.)
As to the low end of the scale, I suppose that instead of -1D2, you can just have -2. That way you don't have to roll the dice. Otherwise, the way I do 1D2 is simply roll D20 and consider 1-10 to be 1 and 11-20 to be 2. You can use a D6, D8, D10, or D12, but I like D20 the best.