Hexagram characters begin with stats rated from 0 to 3, using the arrays I originally developed for Gravity Sinister. (There is a random determination table for players that do not like to bother with making choices.) Then, each level, including first, players choose one stat to improve. The same stat cannot be improved two levels in a row. The max character level is 10, which means that the highest a stat can be naturally is 8 (3 initial + the 5 for every other level increases).
Among other benefits, characters with higher strength scores can wield ever more obscenely scaled weapons. There are three size categories beyond standard: huge, giant, and colossal. They require, respectively, strength scores of 4, 6, and 8, to wield effectively. (Category names are subject to adjustment.)
For normal weapons, strength adds to melee damage, up to +3. Larger weapons can express strength beyond this limit. Huge weapons allow up to +5, giant up to +7, and colossal up to +8. (In general, the max bonus is one less than the ability threshold for the next largest weapon category.) For simplicity, there are no special encumbrance considerations for oversized weapons. Each counts as one significant item. They do, however, cost more to repair (an additional 1d6 * 10 SP per exceptional size category).
Larger weapons retain any type benefits. Thus, a giant axe can express up to +7 melee damage from strength and also provides a sunder bonus to damaging enemy equipment. Oversized missile weapons apply strength to damage rather than perception, but are fixed at +4, +6, or +8, depending on the size category. For example, a huge elephant gun deals +4 damage even if the wielder has 5 strength. Such weapons still use perception for attack tests.
Though this system is designed with big weapons in mind, it would be easy to adapt to enchanted weapons that would only serve worthy warriors (that is, those strong enough or with large enough attack bonus for D&D), and so could be another way to explain and manage the traditional restriction that only fighters can use magic swords.
For AD&D (1E and 2E) ability scores, use the strength damage bonus rather than the Hexagram strength ability. For something like D&D 3E or 5E, use the ability modifier. The mappings are not perfect, but they should be good enough. Some other rulings may be required, given that HP quantities in 3E or 5E are higher that the OD&D standards I tend to assume, so adjust accordingly.
Edit: though above I noted that there are no special considerations regarding encumbrance, I am not fully convinced that is the right way to go. I think as written there may be insufficient incentive for diversity of weapon choices (that is, anyone with high strength would prefer an oversized weapon), which is perhaps uninteresting. I will need to see how this plays at the table, but one potential modification would be for each extra size category to count as a significant item, though I am wary of slipping graduated encumbrance in via the backdoor.