Could possibly get away with 2mm, but with them being 50 profile tyres, and quite low pressures, they tend to bulge, and they're not far way from the "lipless" arch as it is... but as you say - will give it a go for sure!
I'm intending on going on the PNG session as Lee has a ticket for me, and already threatened me if I don't go on, and I want to book another 4 if possible!
Just had confirmation email cah0000000t
"We are pleased to confirm that your 2008 Competition Licence has been sent
for printing today and you should receive your credit card licence within 6
working days."