Very glad that no third party was injured.
I can only go on the above evidence, you said the back end stepped out and the tyres were cheap (tread looks ok from pics, can't see rears fully) and you have been around that bend faster ! It takes some doing to loose control of a car on a bend in the absence of ice/oil/diesel, even with rubbish tyres, it doesn't matter what the Speed Limit is, this doesn't mean you Must drive at or above it nor around the bend at the suggested speed.

I know you really like you car and modding it, but I really think it is not time for you to move up in terms of power, I want to ensure and am sure the rest of the forum will agree that we what to keep hearing from you.