Will u suggest me to buy 7950 or any high end gpu with my this rig?

Hi guys,after having a lot of research i have found that 7850 1or 2,7950 this type of high end gpu will overkill for my demandsi don't want to waster my hard earned money but want performance and long run in other words futureproof(i know nothing is futureproof in tech more than 5-6 years.)
MY rig:PRO:i5 3470
MOBO:gigabyte b75d3v
Ram:8gb ddr3 1333
PSU:CM 550 watt
GPU:HELP ME.
About me:i am a casual and normal gamer.MY RES. 1366*something in 18.5 inch led monitor.i want to play games in normal settings(if possible to run game in high so why should i will miss it).I want to play games about 3-4 or 5 years smoothly without upgrading my system.MY fav games:Sleeping dogs,gta 5,air assault (will be),stronghold 3.mainly i play strategy and gta type games mainly.not others genres much.
MY QUES:
1)as on my demand i need more powerful PRO than powerful gpu.thats why i choose i5.Should i need more powerful PRO?
2)found on net that 7770 or same level card like it will fill up my demands easily,is it TRUE?if true or wrong tell me some name of cards
what about 6850?
3)where should i invest more?
What i want:Run game for 4-5 yrs. smoothly.don't greedy about gaming experience
correct me if i m wrong.
N:B:SORRY 4 BAD ENGLISH
MAY GOD BLESS YOU ALLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLl

Solarstarshines said:

Question you ever plan on getting a bigger monitor at all ?

if yes go with the 7 series card 7770 7870 that will still be good as a 6870 or better the 7870 that is and will run at highest resolutions with a single card

not in 5 years

Solarstarshines said:

I would still get a 7 series or wait till the newest generation shouldn't be too long till a new release

last of this year maybe.