im not really in a position to comment on the viability of either head, but i would have thought that if you were primarily interested in building a race car, then the tried and true method has got to be a winner. experimenting with something and being a bit different is all well and good, not to mention fun and interesting, but you've got no guarantees of a quick car - which the XE head would appear to promise.
as for powerbands, presumably the XE head still came in a viable street 'sports oriented' car - hence i have no doubt that an appropriate selection of cams and headwork you would net whatever result you desired in this respect.