G-14 is good investment upto G-14/4&3 with G-14/4 the best as it has possession. Problems with other sectors including 3 are there are villages or build up property that needs to be removed before any development takes place. In g-14/3 the buildup property is no that big but it is in terms of the size of the sub sector 3. I visited G-14 some months back and looking at sub sector 3 i think it will take time to clean up this place. If you have the capacity to hold till 5 years then G-14/3 is best as prices are low and once you will get possession prices will increase. There are no 4 or 5 marla in G-14/3 that you can find in G-14/4 while 3 has 7 marla and that are too short in number so i would avoid going for anything that is short in number in a given sector. 7 marla in G-14/4 has the worst location by the way.
in g-14/4, 4 marla = 70-80 lacs, 5 marla = 80-90 lacs, 7 marla = 90-105 lacs.
in G-14/3, 7 marla = 60-75 lacs
gulberg is a completely different story. Its not even in zone 1 so you cannot compare it with G-14. I don't know much about it maybe someone else can help you.
By the way you can also consider G-15 where you can find a 7 marla for 65-75 lacs and a 14 marla for around 90-110 lacs