What New Computer should I get?

My macbook has survived the game for an entire year, and i have always wanted a proper gaming PC, a windows based one. Quite recently (IE this patch) I have started having games where i cant play because of to much lag. and this ain't no sissy lag either. I had around 2000 ping and i have to restart the computer multiple times. Are there any fixes for this (i have tried the ones made by rito) Is it worth getting a gaming PC (not a laptop, i have heard that they suck) and if so are there any suggestions for good computers? The ones i have in mind are these. http://www.ebay.com.au/itm/AMD-Quad-Core-A10-7870K-4-1GHz-Max-Gaming-Computer-8GB-1TB-R7-Radeon-Desktop-PC-/360359011069?hash=item53e71222fd http://www.ebay.com.au/itm/AMD-Quad-Core-A8-5600K-3-6GHz-Gaming-Computer-8GB-1TB-HD7560D-Desktop-PC-/360628152400?hash=item53f71ce850 or this http://www.ebay.com.au/itm/AMD-Dual-Core-A4-7300k-4-0GHz-Gaming-Computer-4GB-ram-1tb-HDD-Radeon-HD8470D-A58-/181829438536?hash=item2a55e10c48:g:wxoAAOSwQItT3GcZ I have never bought a gaming computer before but basically, It needs to be windows based, able to run League of legends, Borderlands and path of exile (not at the same time); Around the $500.00 Australian mark (yes its not much but i don't get that much money) and it needs to be able to get shipped to Australia or (preferably) sent from somewhere in Australia to Perth. Any advice? Tips? What not/to buy? Plz leave all suggestions and that sort of stuff in the comments! Ill need some help!