I did two further tests, but the important one was using an Elgato sourced Hi8 SD 640x480 version which I enhanced with Artemis LQ at 200% to 1280x980 at 25.98 frame/sec, as per your advice. I haven't tried the 100% one with the filter which sounded like it might be faster again. That took one second a frame. So around 3.5 hours, for an 8 minute video, and it went from 105 MB in size to 303 MB. I'll try the increase in resolution using the Avidemux and check the quality.
Did some more testing.
Base video used was an SD 640x480 video, PAL recorded, transferred from the original Sony CCC TR805E Hi8 video cam.
Video was 105MB in size and ran for 8 minutes approximately.
Tested changing from the recorded 4:3 dimension to 16:9 and found no difference in speed.
I kept the 4:3 dimension which was a "black bar" format i.e. the picture was not stretched sideways for 16:9, instead one got black bars on the left and right of the video.
I haven't investigated some other AI PC software video enhancement solutions - if they run on my Xeon 5,1 processors, then it would be tempting to put in a suitable card (likely Nvidia) and run the Mac Pro flat out doing that enhancement in a Win10 PC environment, knowing I could only boot Mac OS on the Mac Pro into a sub OS x 12.6 operating system without removing the Nvidia GPU.. I doubt that would work though on the 5,1's old processors.
200% enhancement: 640=>1,280 (720P) and 300% 640=>1920 (1080P) : not useful from me as I could not get Avidmux to go beyond a 200% enlargement. Finacl Cut Pro X though did that quite quickly.
Time to go from 640 to 1080P (300%) was around 5 hours on the MacBook Pro 2017 with 4GB Ram 560 GPU running flat out.
Earlier I thought I could do great enlargements with Avidemux. Handy that such cross platform software is powerful and free. But also, the video did not look very sharp using both the 200% in Topaz (to 720P) and also 300% - going to 1080P.
The time going from 640 to 1440P (2560 x 1440) was very surprising - around 8 hours. Just but the same time as going to a full 4k at 3840 resolution, 2.1 seconds per frame.
Checking with 16 Bit stills from Topaz VEAI, it was not faster and the sound track was lost. Quicktime imported the frames very easily, but it took quite a while to do so, probably because the files were on a slow external USB 2 drive, the drive speed was the bottleneck. The playback though had the occasional noise in it. I tried to import the files into FCPX but mucked it up - the video only went for a few seconds.
Conclusion
I think I will make the entire videos in low resolution, and then enhancement them. The reason being that Topaz's software is quite new, and while its discounted currently at $200 instead of $300, Topaz says you can get a 12 month upgrade for an extra $200. Which means to me, $500 for 12 months of up to date software. Since the software is enjoying a rapid rate of improvement, it will pay me to wait until its improved before buying it. If they gave me 12 months of free updates, I'd be much more tempted to buy the software.
About the platform for enhancement. Strangely Topaz says the software does run on 2013 and onwards Mac pros. And that it runs on the 6,1. Which means Hasell process are not mandatory - but I cannot check that. Topaz says so in more than one place too. Strange.
My MacBook Pro 2013 could do the job - just do it in batches. If its one hour for one minute of 640k to 4k, and the video is 16 minutes long, I could cut the video into two 8 minutes bits and run it over two nights. That would work, and it would be easy to put them together.
I checked on prices for a PC too and a new clone with an 2080 Nnvidea was around $Au2,000 without a monitor or keyboard - a games quality clone. Buying a used card would safe maybe $200.
Meanwhile an iMac 27" would cost around 33% more, or 50% more, depending on CPU and GPU. the GPU would be important. For me, that would probably be worth it. I also looked at mac minis, and they cost around $Au2,000. But then you have to add a T3 external GPU box for $Au500, plus a GPU. The iMac comes out better value. But a PC gives me the flexibility, but not the quality IMO.
Its a shame Apple never made a Mac Mini with some PCI-e slots. For 25% more than a mini. Gee even two wide spaced ones.