The Sutton one was off our back already - non-league (at the time) Luton beat Norwich (then Prem) in the cup a few years ago.......although in fairness, it wasn't that long ago that both clubs were in the same league as each other and they are similarly sized clubs. Lincoln are also ex-league and for many seasons would have played in the same league as Burnley. Same applies to a lesser extent with Chelsea losing to Bradford - the two clubs had crossed paths before and BCFC have long been an established league side.
Sutton beating Arsenal would be off the scale, far more so than when they beat us.......it would top even the Hereford win over Newcastle in the 1970s or the time that Histon a few years ago who beat Leeds, who in fairness had dripped down a good way by then.