1000 simple bounds checks in memory is extremely fast — even in Xojo.
well you can check for yourself what the bounds check cost is
build a console app that has them enabled
do a billion operations that would require bounds checks (something on an array that DOESNT get optimized to a static value by the compiler)
compile it and have it spit out numbers for start & end times
then do the same but put in the pragma to disable bounds checking
compile it and run it again
compare
but yeah it is small even in Xojo
but depending on the # you’re doing a large # can / could have a measurable hit
// #Pragma BoundsChecking False
Dim intarray(10) As IntegerDim starttime , endtime As Double
starttime = Microseconds
For i As Integer = 0 To 1000000000
Dim j As Integer
j = intarray( foo() ) // need to make sure this dosnt get optimized out
Next
endtime = Microseconds
Print Format(endtime - starttime, “######.00000”) + " microseconds"
the Foo method just returns 1
not sure if that call would be optimized down to a static inline of the value 1
and how the array access might be optimized if it did
without the pragma : 46260197.07397 microseconds
enabled to skip bound check 
45848988.40405 microseconds
411208.66992 microseconds over 1 billion iterations