REL T5 vs REL T7 subwoofers

Hi gang, just really curious about this. Back when I was hunting for a new sub in 2015, I was asking for opinions on because my decision was coming down to two choices, the Sunfire SDS-12 and the REL T5. The REL had a ton of fans but the Sunfire dealer made me an offer I couldn't refuse. He needed floor space so I got the Sunfire brand new fooner $400.

I was just meandering through subs this week and took a look at the T5 and T7. The T7 is about double the price of the T5 and my question it really worth that? You could actually buy two T5's for the cost of a single T7 which would seem the more logical choice to me. So, what am I missing? Or AM I missing something.

I  just sold a T7 on the bay for $450..its mint w boxes no the T7 isnt twice the need to shop correctly...we all know about cost and diminished returns ,in the  stereo world its baby steps as you move up in a product line.....but in Rel,theres a quality difference between the 7 and 5 ....and a major difference between T and S series in their new products..again it depends on what your end goal is but definately worth the cost of going from  a T5 to a T7 on used market, IMO...if you cant hear the diff i doubt you even need a Rel

Product review: REL T series subs - Richer Sounds Blog | Richer Sounds Blog

Last of the non-‘I’ subs, the T7 is the biggest sub here, and also sees a number of changes over its smaller brothers. As the only front-firing design here, the T7 has an extra trick up its sleeve – a passive radiator. This 8″ speaker works in tandem with the 10″ active driver on the front, giving a wider frequency response and helping fill larger rooms with ease. With a 200w amplifier running the show, this is the one to go for if you’ve got a big space to fill.

Or, it would be if the T series I range didn’t exist. As noted earlier, the ‘I’ iterations of these models have had a bit of extra TLC from the engineers at REL, or to be more specific, their drive units and cabinets have. Running the same amplifiers as the standard T5 and T7, the 5I and 7I have an improved, lighter woofer unit improving the overall timing and response of the sub. The 5I has a larger cabinet with the thicker walls, offering better acoustic damping. Likewise, the 7I goes bigger in cabinet size, giving greater internal volume and helping to give even more sound for your pound.

I have a related but not quite topical question. Forgive me. 
I listen to only classical and jazz on my system. No home theater. I have an REL t/7i with my Tannoy Kensington speakers and First Way J2 amp. 
I hear that two subs are better than one. But is that true for music or only for HT?