I thought stops were held on the broker's server and only stop limit's are held on Globex. So if IB is lagging in a fast market, it makes me believe that a market stop would trigger later than it should, and that would give me more slippage than potentially another broker? However if a market stop is held at Globex, than obviously there would be no third party issue. I don't know which is true.
IB does not lag as it is snapshot datafeed to the user. Every tick data feeds lag when it is busy. The feed into IB server is tick by tick so the stops held at IB should go off when you think they should.