For me, a 50% discount is good enough (you get twice for your money, guess it comes down to nice round numbers in the end :P).

75% discount is that reduction applied twice (50% of 50%)... you get quadruple for your money!

I'm not complaining if they insist that you grab the entire bundle when it's 75% off (still gives you plenty of leeway to get better than that 50% reduction for the games you want).

It really comes down to basic arithmetic:

Look at the price of the bundle, compare it to the price of the games you want at 50% and figure out which is lower.