my 2c...
The car was designed with a 'matching' tyres front to rear in mind. In matching i mean either 4 road tyres (or similar tread / limits) or 4 semi slicks. I don't understand why you would upset the balance of the front to rear grip by putting a set of semis on the front or rear, and roadies at the opposite end.
wilzlee you even mentioned it yourself - semis have much stiffer sidewalls than road tyres, so that alone can affect the way the car handles, and feels at the limit.
OK so if you say you need more rear traction and put semis on the back, I think the problem is not the tyres but the way you drive. Learn throttle control. You don't see race teams running a wet in the front and a dry in the rear (for example, forgetting about compounds) to promote better front grip - it is a geometry or suspension problem.
A car with sorted suspension and matching tread / compound tyres front to rear will be much more enjoyable to drive than a mis-matched combo.
grepin i'm running 225/50/16 RE55s all round, and they're pretty good. As long as you respect them in the wet, they'll be ok and not try and kill you. I found the worst part of them in the wet is hard braking... they will lock up and slide alot faster than a roadie.
They don't tramline too badly, but i'm running 225s... if you go wider they are alot worse. In terms of front to rear, different tread patterns - like i said above, the best to worst scenario is:
1. front and rear same semis
2. front and rear different tread semis of same compound
3. front and rear same roadies
4. front and rear different tread roadies of similar tread / compound
5. mis-matched front to rear semis / roadies