Gaming Rig Build in Progress

Crucial is great quality RAM. It has a high level of compatibility and reliability. They manufacture their own memory. Unlike most of the other consumer brands. Kingston also manufactures RAM. The other RAM manufacturers mainly stick with OEM sales and sales two third parties like Corsair.

Given that they manufacture their own memory. You're pretty safe buying sticks individually. As long as they are the exact same make and model. They'll likely pair up. Although it is still best to buy a matching kit since pairing is not guaranteed. The problem with other brands is the same make and model chip bought individually may use different components manufactured by different companies. Which can cause compatibility problems, loss of dual channel or reduction in performance to a baseline speed like 2133Mhz. Since they frequently OC the memory to save money and there can be slight timing differences.

You definitely don't want a 2x4GB plus 1x8GB setup. Since there is no chance of dual channel.

The comparison in speeds on that site are hardly useful unless you can find a closer comparison. 2666Mhz C15 memory will obviously be faster than 2400Mhz C16 memory. The 2400Mhz C15 and 2400Mhz C16 are much closer. The small difference can likely be accounted for in the latency differences. If prices are roughly equal. I'd choose the Kingston over the Crucial for the small gains. As far as gaming is concerned. You'd never notice the difference. Along with most other tasks.

If there is a substantial price difference. That money would be better put towards a higher quality motherboard. As you can get cleaner overclocks, higher quality components and/or more features.

As far as an SSD is concerned. I'd opt for a 2x8GB kit first. That way you are guaranteed a matched set. 16GB will make a noticeable difference in some games over 8GB. An SSD will just make games load faster. Since the SSD you can get for the price of 8GB RAM is pretty small. It won't hold many games anyways. I'd hold off on the SSD. Wait until you can buy a decent quality 1TB model. Then you can install all your games on it. The loading time difference is huge. I'd never go back to a HDD for games.