Both 760 and 7950 are almost same performer. The advantage with 7950 is its 3GB memory, perhaps in the future that extra 1GB may be beneficial. Its up to you to decided between the two Graphics cards
The difference on a 1080p monitor is nothing between 2 and 3GB. But in certain situations(like 3 x 1080p monitors) the 3GB will be slightly better, but not much.