While XSPC might not offer the best performing GPU blocks, their Raystorm CPU block is one of the best you can buy. Their rads, at least the EX and RX models, hold their own too.
If starting from scratch, I'd recommend a kit to save a bit of $$. Something like this
. It starts at around $230 and comes with with everything you need to custom cool your CPU. GPU block is extra. It has the Laing DDC 3.25 pump. You can also get it with the Laing D5. Both are good. The first is more compact and offers a bit more head pressure, but may be a bit louder. The second is larger, offers a higher flowrate, but lower head pressure. Both fit inside the Dual bay reservoir.I don't recommend skimping and going with an XSPC pump as found in some of the XSPC kits out there such as here
. The kit in the first link also comes with compression fittings, which offer peace of mind and are easier to work with than barbs. (FYI, on the linked site, you need to place the kit in your cart, then go back to the kit product page
and place steps 2, 3, and 4 (fittings, tubing color and radiator - larger radiators will add to the cost of the kit) A little confusing, but I've found it a good place to get stuff.
A kit like this will save you a bit of money and you don't have to sacrifice on the parts. Then choose a GPU block of your choosing separately.
And regarding single vs multiple loops, contrary to what many might say, I believe single loops have been proven to be more efficient in most scenario
s. They are also simpler to build, easier to maintain. It's a win all around. The only time to go dual loop is if you have a lot of components to in the loop that starts limiting flow. However, A CPU block and up to 2 rads and 2 GPU blocks, as long as they are of the newer lower-restriction designs, it's single loop all the way.