Could you be more specific please. Did you go wider than you had before, and went faster too? I think that's the big question here.
Also which casing did you use? The standard, or the reinforced version? I'm going straight to the lightest one to see what this is all about.
Ok. This might be long.
I run all of these with tubes, because it's easier and I'm allergic to latex. So I don't want to use latex sealant.
I've run RH Extralights on my gravel bike, 700cx35, and 650bx42 and 48. (in that order, obviously new wheels between the 700c and 650b). I also threw on a 48mm Gravelking TLC on the rear for a few hundred miles when I needed a local replacement between the 42s and 48s. It also had a couple of other pairs of tires on it for a ride or so before the RH ones came in.
The tandem has had (last 5 years anyway) some Schwable 26x40mm City Jet (kevlar) on both ends, then RH 26x44mm Natchez Pass EL (front) and 26x53 Rat Trap Pass Standard (rear), then a new set of Standard weight, same sizes, and now due to failure I'm running a Schwable 50mm Kojack on the rear. The 44 is as big as I can fit on the front with fenders, and the RTP is about the same on the rear.
Performance wise, the only apples to apples comparison I really have is the Schwable -> RH transition. The tandem went from ~15.75mph average to 17.25mph average over ~6 similar rides on either side of the change. The previous max average speed for a ride was in the 17.2 range, so there was a significant step jump there. The only other changes at the time were new fenders with better clearance and new bar tape, so I don't think that either of them were a significant contributor.
I don't think I've been able to tell the difference between the EL and Standard on the tandem, but I've never gone straight from one to the other.
I'm not sure about the Kojack though, because it went on at the end shoulder of the season and fitness changes make that difficult to tell. We're certainly not as fast this year as last year, but that's training as much as anything. Running the RH tires at 45psi is certainly more comfortable than the previous ones. 45 psi is basically high enough to avoid pinch flats on driveway curbs, and high enough that the stoker isn't bouncing. I have to go higher than that on the rear when I have a slightly heavier stoker (70 vs 60kg).
Some things to consider:
I've had 10 of their tires. 3 are still on, 2 were retired with some life left due to the wheel change. 1 was pulled off with minimal life left. That leaves 4 failures, 2 RTP, 1 Babyshoe 42mm EL, and 1 Nachez Pass. The Nachez pass died after a good life when there was a particularly bad puncture that cut the threads, and the carcass started to pull apart. Had to boot the tire for the rest of the ride, but the tire was done for after 3k miles.
The other ones though -- could have been doing it wrong, could have just been that they're delicate tires. The rear 42mm tire developed a sidewall failure where the carcass essentially started to split along the periodic cross threads that hold it together. This led to cm long frizzy bits in the threads, which ate into the tubes (due to flexing) and eventually split the threads, so the sidewalls were cut. This was probably me running a super low pressure for most of the life of the tire -- basically avoiding noticable squirm under cornering and pinch flats, but significantly below where their tire pressure calculator would say for the low end. But it was comfy. This was ~2700 miles into their life, so not significantly short, but they could have gone longer.
The RTPs both failed when the sidewall started pulling away from the bead and delaminated. One lasted 2500 miles, one only 1k. I'm pretty sure that what happened here is that the tire didn't fully seat, and there was about an inch where the bead was stuck inboard on the rim, so the tire was bent over the bead more sharply then it should, and that lead to the outside threads fraying and then failing. After the first one, the dealer recommended higher pressure -- but that didn't really go well. They also insist that the brakes damaged the tire, but I'm 100% positive that wasn't the case. I think it's just that the 25 yr old rim that I had (with Velox Fond de Jante tape) just wasn't letting the tire seat properly.