The 4x10 is rated the same as the 1x15 ie 250 watts at 4ohms, so they'll both need an extension cab to get the full 250 watts. However, I very much doubt you'll be struggling for volume with either. Photo of a page from the SMX brochure attached.
The previous Trace ranges (MkV for example) used to quote 165 watts for a 250 watt head running at 8ohms.
EDIT - Obviously speaker surface area also comes into play when choosing between the two but others can discuss that at far greater length than me! 😣