Tires: Mixing of Speed rated Tires, goodyear eagle rsa, toyota matrix xrs

Question
I have a Toyota Matrix XRS and I bought 2 Futura 2000 LTE tires(205/55/16, T-rated tires) from Pepboys. All the tires before I bought these ones were Goodyear Eagle RSA(H-rated). At the time of buying I did not much about tires and I just bought what Pepboys showed me. Now when I had to replace the other two older RSA tires at another Pepboys store they said they would not have put the Futura 2000 LTE tires on my car which their other store did because mixing of speed ratings makes the car unstable. I had noticed that in the past weeks since I had got my tires rotated, the T-rated at the rear and the older H-rated to the front but I thought its just due to the height of the car. The Matrix is a small wagon. I would not purchase from Pepboys again. I want to replace the 2 older Goodyear Eagle RSA tires with Yokohama AVID V4S (V-rated) at the rear and the front 2 will be the Futura 2000 LTE (T-rated). Is this dangerous ? And what I have at the moment that is the front 2 tires T-rated and the back 2 tires H-rated, would this make the car unstable or unsafe to drive ?  

Answer
Where this becomes an issue is when you do emergency maneuvers and it's possible that the vehicle will become unstable and spin out.

Of course going to V rated tires is going to make matters worse.

But this is not a "black and white" - "safe / unsafe" kind of issue.  It's a matter of risk, and this has to be balanced against the cost involved and how much risk you are willing to accept.