Hmm
I'm sorry to hear that, especially that it even did/does the lagging on the stock Moto ROM.
It would be premature of me to say it sounds like a hardware issue, but it seems like thats the path most taken when evidence like which you provided is given. Multiple ROMS, no excessive programs/apps running and it still happens.
Not sure what your situation is with returning the X for another one, but its probably out of the scope now since you mentioned you've been on several ROMs. I'm definitely not stating you're a n00b because you present yourself with valid concerns.
But I suspect it could very well be hardware related. It has definitely been an issue over the course of Motorola products. On my D1, I had the best of luck. I could run any ROM, any kernel, overclock it to ridiculous speeds...no issues whatsoever. My best friend got the same phone, same day, same store. Brand spankin new...nothing but issues with his.
I hope some others can chime in here and offer some potential helping advice cuz I'm at a loss right now.