Keep it the same on the springs so the alignment is the same and you should end up with a slightly higher gearing - don't forget to recalibrate for the odometer error caused by the larger tire circumference.
Skirts - Yep, they stick out in the rear enough skirts are out of the question.
It feels like I got a higher gearing just from listening to the engine. I use a GPS and it reads pretty much the same as before. Low speed is right on and around 60mph on the speedometer it is actually 63-64mph. If I put lowering springs on I know they would rub under load since they fill out the wheel wells. Honestly, the handling difference makes up the MPG difference if it is only around 1 MPG. I can live with that. If they drop me to a consistant 35 MPG than they come off! BTW, I'm running 50psi all around.
My experience with 13 years of Metro ownership (owning one since new and we just sold it) was dorking at all with tire size and quality had a negative effect on FE and performance of the car (acelleration).