I'm assuming you're referring to the Silverstone SST-ST50F-ES @ 229. In this case, the Seasonic Silence Pro 500W would by far be the best choice as the Silverstone Strider Essential SST-ST50F-ES is made by Sirtec which is a very lackluster build. Go with the Seasonic Silence Pro 500W, but just so you're aware, it uses an 80mm exhaust fan compared to the usual 120mm intake fans on most psu's.

The general order with regards to the 3 psu's and their oem's are:
Seasonic>>FSP>Sirtec

*Note the extra emphasis '>>'

Correct me if I'm wrong, but your CM EPP 500w has 2 12V rails (18A + 18A) but could only give an output of 360w? On Anandtech's review, a total system load running something like furmark would net ~320w for the 6950 system and ~350w for the 560 Ti system. This is with a nehalem core i7 920/930 with almost nothing else in the system. I don't know what you're currently running, but my gut feeling tells me you're gonna overload the 12V rail and if not, you're gonna come so close to redlining it that your psu's gonna burn out or shut down real soon. I would recommend you get a higher rated PSU if you were looking to get a 6950 or 560 Ti. When you do, pay attention to the amps on the 12V rail. Ideally, multiplying the Volts with Amps should get you close to the rated wattage on a good psu. (Example, my 650W psu does 54A on 12V line, 12*54 = 648, which is close to the rated 650W). A quality 550w to 600w psu should do fine with a bit of overhead safety.

If your retailer only has CM psu's go for the Silent Pro M 600w or 700w, those are good units built by Enhance. I think the Silent Pro M 600w should be around the same price as the GX 750w.

Between the ones previously listed and around that RM200 mark, the Gigabyte Odin GT 550W @ RM169 you're looking at is a good build and one of the best bang for buck and proven options. If you don't mind though, the 12v rail is 'split' into a total of four 12v rails mediated by over current protection, so it may require you to organize your power distribution in order to not overload any rails and trip the OCP mechanism. Aside from that, everything else is solid (including the price ).

Good modular psu @ ~RM200, not that I can see. You've been spoiled with the Odin GT @ RM169, just be aware that it's not common to see something like that go for that kinda price. You'll have to see what's available locally to you and decide based on what you can buy there, unless you're willing to buy online.