Need Kt88s Genelex? or Shuguang?

What aspect are you trying to 'up-grade'. Tone? FR? Clarity?
For example, I use SED KT88's on one amp which may be a tad needy of some upper bass warmth and a little upper mid's and highs 'sparkle' but I use SED 6550's in another amp where I need tighter deep bass and linear tone thru the mid's and slightly soft highs.

I think it will help you in your search if you take a moment to define what you are looking for. There is no 'best sound' - its a matter of taste and synergy. FWIW the SED's are about as rugged and reliable as a family of tubes come.

Newbee, good points. The midrange is currently on target with my preferences - lush and detailed. I'm looking for more mid and upper bass definition, more lower bass impact and more extended (sparkling?) highs.
The McIntosh-branded Electro Harmonix tubes that came stock with the 275 were nothing special and developed the "blue pulsating glow of death" after less than 500 hours. So, durability is an issue.

The reissue KT88 Gold Lions may be just the ticket for you. I've read about the reliability issues. Sonically, as they have been described to me, they may be just the ticket. May be. I've not heard them in your amp. I would suggest that you would want to buy them from someone who carefully screens/tests the product and will stand behind them. In that regard, look up Jim McShane - he posts on Audio Asylum and has an outstanding reputation. He also has a history and you might discuss your situation with him before any purchase. Good luck........

I'm extremely happy with the KT-88 Genelex Gold Lion reissue. I've had them for about 6 months. They're great tubes, top to bottom. My amp is a Music Reference RM-200. Solid bass, mellifluous midrange, excellent on up, very nice all around. They're a big step up from the stock tubes (branded RAM but I believe they were fairly generic chinese tubes). I don't think you can go wrong with them. Jim McShane is a good guy, btw, and knows his tubes. Triode Electronics. Or any number of places sell factory matched quads. Jim McS's matching may be more precise than the factory matching.