I'd put my money to work for better bang for the buck speakers first of all, as well as that overpriced and underperforming sub. Some reason you're getting a 9 ch avr for a 5 ch setup? That 70.4 avr is rated at 140w/ch in stereo, especially compared to the 7 ch 50.4 which is rated at 135 on the same basis. That's barely different, it takes a doubling of power to increase spl by 3dB, 5 w/ch you won't even be able to tell the difference. It's the feature set in the avr you should be concerned with. Certainly not something that will be different in terms of "opening up", for the rated 200w capacity of your mains; you'd probably want outboard amps on either avr if you want max capabilities. Who the heck is trying to sell you on all this nonsense?
The VT50 got great reviews, I wouldn't worry about the minute differences for the newer models unless they're very important to you.