My i5-4750 with 8Gb RAM seems working fine with html5. But I still prefer how game looks in flash version.
My concern is more about the bigger memory usage by the HTML5 version. I even suspect there is some kind of memory leak because over time the memory usage increases, especially when doing NH rounds. At work I only have 8GB and can run only one account no matter which browser I use. At home I have 16GB and can run several accounts at once but even there it get sluggish when using several HTML5 sessions.
I just made a little test on my secondary "snail machine": i3-3220 (Quad-Core), 8GB RAM, GT710 GPU, Win7 64bit, FF Quantum 60.
Both in HTML and Flash, RAM usage is at the same level and constant (+/- 5%), no matter whether I'm idle in the game or doing some activities (I loaded 20 neighbour towns each).
I only see a big difference in CPU usage: in Flash mode, idle level is at 5%, while it is at 15-20% in HTML5. Peaks going up during activity are also slighly lower in Flash (+/-5% less than in HTML5), in both cases max. 50%. Although not critical, I don't really like this HTML5 behaviour - why should I waste more energy in idle state ?
Also noticed now that graphics problem on HTML5 in OPERA are still there like since the beginning: there seems to be a milky layer all over the screen. This is NOT the case in Firefox !
Besides CPU and RAM: is there a different behaviour of Flash vs. HTML5 in terms of transfer of workload to the GPU ? If that is the case, one should also have a look at the graphics card used (integrated or separate) and the amount of allocated main or additonal own RAM ?
EDIT: Exactly same happening on my i7-2670 (Octa-Core) with 8GB RAM, but with lower absolute values. RAM constant, only CPU usage higher on HTML5 than Flash.