my issues with the Onkyo 606 was the upscaling other video (it does 1080 p pass through) like my Tata Sky (where I watch my premier league etc.) to 1080 i whereas the HK AVR 255 upscales it to 1080 p
I don't watch too much of the premier league but have seen couple games. I believe a simple test will put your doubts to rest.
Without the AVR hooked up, connect the video out from the sat cable box (HDMI or component) to your TV and check the resolution.
If it says 1080i or 720P, then there is nothing for you to do but just hooking up your Onkyo for HT
If it says 480i then you can only "upscale" to 1080i or 720P. There is no way you can get to 1080 P.
Besides all the fuss about 1080 P, did you know that you get the best resolution (optimal picture) ONLY for 1080P 24 frames/sec refresh rate or a multiple of it is required. Otherwise your TV is scaling down the pic even if your AVR shows a 1080P upconversion.
Now my dilemma is whether this difference is significant
Based on my comments above I would be very surprised if you saw a difference. But we will wait for your test results as its all in the eyes of the viewer.
am I reasonably future proofed or not.
If you see the history of how "future proof" we all have been, then for electronics its a total myth as we explore the "next best thing". The most notable examples of where we are future proofed is our homes (if you own one) or families as wedon't tend to replace them as often.
Back to your original Q,
The list below are some TVs that support 1080p 24 fps and even they are fraught with quality issues. also see no Samsung or LG though some newer ones in the last 6-9 months have supported these. The list is about a yr old though.
Hitachi P50X902 (48HZ Plasma)
Hitachi P50V702 (48HZ Plasma)
Hitachi P50S602 (48HZ Plasma)
Pioneer Elite Kuro PRO-101FD 50 Plasma (72HZ)
Pioneer Elite Kuro PRO-141FD 60 Plasma (72HZ)
Pioneer Elite Kuro PRO-111FD 50 Plasma (72HZ)
Pioneer Elite Kuro PRO-151FD 60 Plasma (72HZ)
Pioneer Kuro PDP-5020FD 50 Plasma (72HZ)
Pioneer Kuro PDP-6020FD 60 Plasma (72HZ)
Following plasma's though support multiple of 24fps caused some crazy flickering and were replaced when someone complained about it with a true HD signal (blu-ray or HD DVDs)
Panasonic TH-58PZ800U (48HZ Plasma)
Panasonic TH-50PZ800U (48HZ Plasma)
Panasonic TH-46PZ800U (48HZ Plasma)
Panasonic TH-42PZ800U (48HZ Plasma)
Panasonic TH-65PZ850U(48HZ Plasma)
Panasonic TH-46PZ850U(48HZ Plasma)