The specs where iPad Pro trumps Surface Pro 4?
I think "specs" also cover things like amount of storage, amount of RAM, SD card slot, and bunch of other things than just CPU power. I think this is where SP4 has real value advantage over iPad Pro (especially the Core M version).
I, like you, find the A9X CPU power beyond impressive, but when it is only applied to iOS apps, I'm not quite sure why they are spending that kind of effort honestly. When a lowly Atom CPU tablets like Surface 3 can give you lag free drawing experience, A9X isn't really necessary for the task. I'd much rather see the effort spent on iPad Pro features on a 10" form factor. That would make it easier for me to suggest the purchase for my Apple only friends who like to draw on the go. Right now the 13" form factor seems too unwieldy for a lot of them.
With all the money and effort going into CPU development, you'd think Apple is in the process of porting OSX to ARM, lol. Hmmm... maybe that's not all that crazy...