The Samsung 25R is still one of the best batteries out there for the money... The Tiffany Blue ones or the new Green 25R5's are the same specs, and should be fine for your SubBox (I'll assume 50W version, but will also be fine in the 75WTC MOD). I've had a couple Samsung's go south on me in the past year, but that can happen to any Li-Ion cell... Of the more than a dozen I regularly rotate through, even the ones I purchased 18-months ago are still going strong. For me, I cannot recommend the 25R enough, although I also regularly recommend LG's HE2 and HG2 as well, but for the price, you cannot beat Samsung.
I'd like to know about these as well... independent test results, etc.... to my knowledge, no battery has been independently tested to provide higher than 30A continuous discharge, so I'll assume 40A is the pulse-rate? There are plenty of other batteries out there with higher pulse-rates, and that is not an indication of of their sustained discharge or safety. Furthermore, as mAh increase, discharge-rate (Amps) decrease... it's just a fact of physics, so my guess is these 3000mAh batteries are likely 20A (or lower) continuous discharge....