for example hearing the size gains are way better for 750mg of test vs. 500mg of test but the strength gains being the same, shouldn't the extra size provide more strength?
this seems to be true with a lot of different substances.
Larger dose of gear can help you gain more strength, too, everything else being equal. Some substances are particularly useful for strength gains. Tren, D-bol and Anadrol all send strength through the roof when used with Test, the last two adding a lot of size, too. Albeit much of it water. None of this means much if you aren't eating and training right, and getting plenty of rest. You can gain plenty of strength and size on Test if everything else is in order. Muscle Hypertrophy has more to do with your training methods, and as CT already stated, your diet. Size does not always equal strength and vice versa.