I'm running some Tung sol 6550s right now because I couldn't get a hold of any SED 6550s. Everyone seems to rave about the winged C's but the Tung Sols are quality, and a fraction of the price to boot.
Get with Laura (ValveQueen.com). She will hook you straight the fuck up. I got a set of Ruby 6550s for my Diezel VH4--killed 40062 people in 9 counties.