I see the problem, there is big jumps in their product lineup: GTX740 is no better than the current GTX280 in most respects. R7 360 is a good deal faster but isn't as good at streaming as the even faster (and more expensive) GTX950, which will be noticeably restricted by the Q6600. Quite a conundrum.
Suggestion: Start another thread, something like 'Q6600 steaming CS:GO: R7 360 or GTX XXX?' there's plenty out there with far more experience than me on the subject of streaming so I'll defer to their experience and knowledge.
Suggestion: Trust my comments and grab a GTX950, it WILL be significantly held back by the Q6600 (even if you overclock it) but you could carry it over into a system upgrade a little later on. As a combination the Q6600/GTX950 will greatly extend the range of games that the system can reasonably handle: My own Q6600/HD7950 reserve/backup/retro gaming rig can still play games like the recent Tomb Raider reboot and the Metro series with only a few stutters in the most demanding sections, all caused by the CPU BTW.
Final suggestion: Look for a GTX750, personally I think it'll be the best overall fit for your sons needs and the extra GPU power will extend the range of games he can play on the current system.