I would say since you're using a sub, use the 65T's (or Monitor 60's). Save that money. I say this as someone who has all of the monitor line. I have several M50's, M60's and M70's.
My reasoning is that you're using a sub to perform 80hz and below, so extension from the mains is not needed. All you need is mid-bass, mids, and treble from your mains. Unless the room is massive, three drivers will be able to produce that, doubled. Also consider the 75T's (or M70's) also take more power to have everything going at it's best. I wouldn't just rely on your receiver to adequately put everything into those 10 drivers between those two mains if you went 75T's, so it would add to cost to consider an amplifier beyond the AVR (and of course also require your AVR have pre-amp out units).
With that saved money, get a second sub.
Source: Pioneer VSX1121
Fronts: Polk Monitor 70 x 2 (AudioSource AMP100 in bridge mode, each)
Center: Polk Monitor 70 x 1 (AudioSource AMP100 in bridge mode)
Side Surrounds: Polk Monitor 50 x 2 (Direct from VSX1121)
Rear Surrounds: Polk Monitor 50 x 2 (Direct from VSX1121)
Subs: Polk PSW505 x 2