1) 5687 have good servicable lifespans comparable to most octals. 9 pin minis usually last a little longer then octals (this is a gross generalization, of course), so you can say 5687 aren't as long lived as most 9 pin tubes.
2) It's hard to say how much of an impact the 5687 will make on your gear. It depends on how your gear is designed. If the 5687 is used as a high gain device, it will have a big impact on the sound. If it's a low gain driver, it'll have less of an impact.
3) Raytheon 5687 are nice tubes, and actually my favorite 5687. It's the most tonally neutral of 5687s in my gear. The Raytehons also have some of the best spatial seperation for htis tube type. All 5687 are relatively warm, full, and dynamic. The Tung Sols are the smoothest (especially the ultra rare flat plate variety), the RCA bronze plates are the warmest (big round bass), GEs have a more aggressive treble, the regular Sylvanias are solid performers with nothing really noteworthy about their reproduction, while Sylvania Gold Brand are fast and one of the most neutral 5687, but some regard it as lean. How was that for a run-on sentence?
2) It's hard to say how much of an impact the 5687 will make on your gear. It depends on how your gear is designed. If the 5687 is used as a high gain device, it will have a big impact on the sound. If it's a low gain driver, it'll have less of an impact.
3) Raytheon 5687 are nice tubes, and actually my favorite 5687. It's the most tonally neutral of 5687s in my gear. The Raytehons also have some of the best spatial seperation for htis tube type. All 5687 are relatively warm, full, and dynamic. The Tung Sols are the smoothest (especially the ultra rare flat plate variety), the RCA bronze plates are the warmest (big round bass), GEs have a more aggressive treble, the regular Sylvanias are solid performers with nothing really noteworthy about their reproduction, while Sylvania Gold Brand are fast and one of the most neutral 5687, but some regard it as lean. How was that for a run-on sentence?