When I said,
Can a handful of S300/400 sytems hold back the Israeli Air Force? 
What about a Israeli/US/British offensive to destroy the Iranians Nuclear capability? What about just a US/British offensive? 
What about the change in Russian Foreign policy? would they put there "Military Advisors" at risk of American/Israeli/British warplanes?
I did not mean, 
an invasion of Iran.
Please dont take what I said as an Invasion, I ment a Sustained 
Air Offensive, Not Paratroopers landing in Tehran. I'm sorry if you interpeted it that way.
When I say Offensive I was referring to an operation like Linebacker I/II, Not Operation Overlord. Even though you are correct, we were talking about an Israeli premptive strike, not a joint operation.
I'll leave you with one question, before I sign off, Do you think it would be impossible for the Israeli's to destroy any Iranian Nuke Plant/Facility in one quick "suprise" Strike? 
Nice conversation GScholz, I'll be sure to check in on this thread later, after I get some Zzzzz....