Well the best bet to get to 5ghz is with the i5 2500k or 2550k. I would wait for Ivy Bridge to see what kind of overclocking can be done. The current i5s only have a "chance" to get to 5 ghz. 4.5 is easy if you think that will do.
What are websites that send to Malaysia so we can do some pricing for you?
5.0 GHz? That's a hefty overclock. In that case, go with a better CPU cooler (something other than Hyper 212 Evo)... in fact, I'd recommend liquid cooling. Maybe an H100? Keep in mind that overclocking to 5.0 GHz is going to take some oomph off of your other components (like your GPU).
The hyper 212 evo will not do it. Something like the Noctua NH-D14 would do it. H100 is crap. If you get liquid cooling you should just make a custom loop. That costs a pretty penny and would really cut out from components. if you get the NH-D14 that would be your best bet. But we need to see what websites he can use before we can see prices.