Well, I know that this post will probably leads to nowhere for several reasons. I haven't stated what what my goal was, or what kind of knowledge I have and also I don't have my mind cleared of what I really want to do. Also when it comes to decide what to buy, each one of us have different opinions and as there is a such huge offer in the market, it will be really difficult to choose any platform.
When I talked about to be 100% Linux compatible I meant that the platform should be able to accept third party software to compile and upload programs and was that third party software that would have to be 100% compatible with Linux because I have been trying to compile a small .c program written with Arduino C like code and avrdude complains about undefined functions such as Serial.begin or DigitalWrite or AnaloRead... This obviously has something to do with not included .c heders (.h files). And for some of the functions I know how to solve the problem but for functions such as Serial.begin or Serial.println I do not know!
About the heavy load tasks I talked about, I was thinking about bitcoin mining. I know that pior to 2013, FPGAs were used to this. After that Asic chips were developed and FPGA's are no longer profitable. Anyway, but if I went to this subject, I would only want to see an FPGA's "doing" bitcoin mining, it was not to be doing it for long time. As I say, just to see stuff working.