The engineering and adjustability of modern pedals makes them very difficult to compare to a 50+ year old design. Speed Kings are great and were a staple for many years, but there's no doubt they have been surpassed.
That is not to say that they are not playable or that they aren't good enough for the job, but check the adjustable features on the Demon Drives, Axis, Trick, DW9000, IC's Elims etc....you'll find they just don't compare.
If you like the feel of it, use it.