REL T1 or T5? apples to oranges?

Hello - I'm in the market for a new sub, and am interested in REL. Unfortunately, my budget is rather small - about $600. I will use this in a system for both music and HT.

Comparing the T1 to the T5 may not be an 'apples to apples' comparison in terms of size and specs for these subs, but since the T1 is a little older and (I think) being discontinued, it can be purchased new for about $100 less than the smaller T5. So the reason for the comparison is really comparable price tags.

T1 - Larger 12" driver w/12" passive; 300 w; older model
T5 - Smaller 8" driver; sealed box; 125 w; newer model

For roughly the same price (in the new-purchase market) I can get either of these. Any opinions as to which is better? Seems like the T1 would be a better deal, but does the fact that the T5 is a newer model make it a better buy even though it's smaller? (ie: is the newer smaller model better than the older larger one?)

I know room size matters, etc But, I'm not expecting/wanting this sub to lift my house up or even rattle the windows. I want quality over quantity here, to go with my current, very modest system:

Rotel RSX 1056 Receiver
Oppo BD83 BluRay player
DirectTV HD DVR
NHT SupperTwo mains
NHT Center & Surrounds (5.1)
NHT SW10 Sub (now deceased)

Any thoughts, suggestions, comments would be most welcome! Thank you all very much for any help you can offer.