I'm running 175/70/14's on 4 1/2" MGB wires. I've lowered mine 75mm at the back and 90mm at the front. I didn't have any problem with the front outriggers fouling, but needed to move the bulkhead back 20mm and 'adjust' the front faces of the footwells inwards slightly with a lump hammer to get the front tyres to clear -
The lower you go at the front the more likely the tyres are to foul the bulkhead as it's angled forwards towards the top. Phil J hasn't lowered his cars quite as much as I have and is able to use 175/80/14's without any clearance issues.
I rather like the look of the taller tyres and I'm going to raise my suspension (and put softer springs on the front) over the winter so I can fit some to mine, both for the looks and to soften the ride a little, which blurs your vision on rough roads at the moment
. Although I like really low cars I don't think a slightly higher ride height spoils the Spyder shape at all.