The block in that kit is as good as it gets for the most part.
The thickness of the radiator is very unimportant in a way... meaning that a thicker radiator isn't usually going to substantially outperform a thinner one. It will most likely like different fan speeds however and it is important that you read the shootouts of that radiator vs another.
You do not need the most expensive parts imaginable.
The price difference to upgrade from the Rasa750 pump to the D5 is really not even worth it in that kit so I would recommend you buy the Rasa750.
I have used the Rasa750 in a setup with 2 radiator the raystorm cpu block and a maze5 universal GPU block and it had plenty of power. The price difference between the 2 kits would mean that if for some reason later on you needed a new pump you could just grab a D5 or DDC style pump and throw it in without it costing more than the D5 kit would have cost in the first place. You can retain the Rasa750 pump/res in the loop with a D5 or DDC with no downsides at all and it will increase your flow rates and safe guard you from pump failure.
You might not really need 2 2x140 radiators. While gaming your CPU won't be creating the amount of heat it would while stress testing and while stress testing you won't be using your GPU. Also haswell core temps might get very very high but it isn't really dumping a lot more heat into the water loop itself it doesn't have a significantly higher TDP it is just about the same TDP (a lil more) but in a much much smaller area which is why it gets to 100C so easily.
Anyways what I am trying to get at is you are complaining about cost but you can buy the Rasa750 EX280 kit for $169.99 and it comes with everything you need except a GPU water block and 2 fittings for the GPU water block.
Also while stress testing it shouldn't matter if your system is loud so while stressing you can crank the heck out of your fans which will keep the water temps very low. Also the hotter the water gets in relation to the ambient temps the more efficient it becomes at cooling the water. I really think that with a budget you should grab the EX280 kit. If you really want 2 radiators then grab another EX280 radiator not some expensive thick radiator.