I live in Bangladesh.Why do you prefer i5 combo?
Ok, don't know any good webshops there, I'm afraid.
I'd choose that combo as the i5 is generally a much better than the i3 and the 5850 will be extreme overkill at 1280x1024.
However, if you are planing to upgrade your monitor soon as you said, the i3 combo might be a better choice for gaming. For certain games that only use two or less cores the i3 will actually be better as the clock speed of the i3 is much higher.
What is the availabity when it comes to AMD over there?
There are several AMD CPUs that are better choices for gaming than the i3 and that also cost less.