I change my Odyssey's low beams to 4300k and left the foggies stock. My Civic has 6000k and I feel the 4300k might be the best compromise between output and visibility.
FGK is short for Fujitsubo, AusAccord and aka_NSX has the FGK Wagolis, Atjo and I have the HKS Legamax Premium although mine was for the Absolute model and needed modifications to fit. The Youtube you saw was most probably Atjo's system. Another member Mobil1 had the HKS hiPower 409 and that one was loud. Most companies only make cat back systems for the RB1, might be a challange to find a header.