I just ended up the round up of various SS7 cpus at 250 mhz.
At first I wanted to use the Aopen AX59Pro but there is no way to make it stable using the nvidia geforce2 mx 400, so I switched to the Epox MVP3G5.
Every frequency has been achieved at 2,5x100 (except for Rise that was at 95x3), I wanted to include the k6-2+ and 3+ but there is no way to set the multiplier 2,5 so I left them out.
For k6-2 CXT I used the 500 mhz version.
Wattage peak has been misured during dos benchmarks.
Here are the pictures of the competitors: https://imgur.com/a/oPLriqZ

Results:

Rise cpu was a nice surprise, very low power consumption and very cold, it was under 35°C even under load, too bad it just won't run at 300 mhz, after the first bios screen it become garbled, I decided to include the 285 mhz since I due to it's fragile pcb I think I won't stress it again for some time.

On the other side, Cyrix, I can confirm that they are hot like an oven and that the v2.2 version has lower performance compared to the v2.9\2.7.

Amd: the difference between the k6 and k6-2 clock to clock are weird, in dos test they had the very same results, while in Windows mainly in 3dmark99 the difference is huge (it probably take advantage of 3dnow instructions). On the other side I don't know if the 500 mhz cpu I used was unlucky or what, it's weird that it had lower performance compared to the non cxt version.

Intel: The pentium mmx shows how things goes when program are optimized for a specific cpu or not. Great results in Quake, but very bad in alu programs, I was curious to try the tillamook, but since the one I have simply doesn't work, I had to use a mmx 233 overclocked.

I'd be curious to try a Idt winchip 2, but unlucky I don't have one.