It's not so much the brand of the DIMMs as the exact chips used to make them. Corsair doesn't always use the same chips for their value RAM, so it would help if you can give us the part numbers from the chips. If you give us those and the specific part number of your Geil RAM (and from the chips on it if you have the new sticks already and there are no spreaders) someone can probably give you a good idea of how they'll work together.
As SewerBeing said, you'll need to find one set of settings that works for both pairs of RAM. If you're lucky, that will be the ideal settings for one pair, but you might have to run both pairs with less than ideal settings.