The resistance is not really any issue: using feeler gauges in this application is a 'go / no- go' process and not one that depends on feel. Setting ignition points in the olden days with feeler gauges (anybody remember how terrible that was- I do not miss it one bit) did depend on feel because you could force the points open with too big of a feeler gauge. But checking engine valves is different because you cannot force the valve to open to permit a 'too big' feeler to go in-between the cam and the follower (bucket). So if a given size goes, the gap or lash is at least as big as that gauge; when you finally try the 'too big' gauge it simply will not fit (the 'no go' size) and the gap is something smaller than that feeler gauge. So you can push as hard as you want on the feeler gauges when checking valves. The final limitation will actually be the feelers themselves because they will buckle.
Brian
That is exactly what I was getting at but could not think of a better way to say it. What I am concerned with is the spring pressure caused by "bend[ing] them somewhat". How much does this spring pressure add to the resistance felt?