I think Dan (Ekona) has given up on these threads
Long and shot of it is .... Yes, you can have four totally different tyres on you car.
Thing is, it makes your car feel awful. So why would you?
I recently altered my alloys and tyres. Took it back to standard. I took Ekona's advice and bought some M PS2's. Which were (for me) VERY expensive.
The last two weeks of driving since they have been fitted have been some of the best driving I have ever FELT in my life.
Positive, flowing feedback, planted car, fantastic grip. And that is just "normal" driving.
Same car, same roads, same driver.....
I KNOW this is JUST down to my tyres. (70% tyres, 30% alloys) I will never go back to mediocre or even "top" quality tyres. I will only ever have the best tyres for my car. Yes it costs a lot, but when it transforms your car and makes your experience into something so much better... Why would you do anything else?
At the end of the day, it is down to you.
Hope that helps