increasing the lift on it's own is a surefire way to kill the lifters on the XE - the profile already has a fairly agressive acceleration and the lift already requires piston pockets - many users of wilder cams with standard pistons report excessive tappet noise afterwards.
Also, increasing inlet valve size in the XE should be one of the last things you do - and only on an engine built to take advantage of the extra flow above 6k rpm
concentrate on the head - there's plenty of potential in there - but there's no major restriction in one area that will give a large gain -it's more a case of paying attention to detail and small gains all adding up - the exhaust tract though is especially restrictive - and would show power gains if you had a well matched manifold - don't ever match the exhaust ports to the manifold though if you intend to build a well tuned NA lump - reversion is discouraged by having a good step in diameter.
he wants to know about heads Matt, not anal polyps
the exh. ports are always generally badly mismatched to the valve seat - all the heads I've seen always have a ridge on the plug side of the port, just below the seat, and another lump on the small radius of the tract.. in general though the ports can be opened out a little too, as the seat is generous and can stand a little opening out.
duration is what makes power really. having the valve open for longer gives a better power increase than having it open for the standard duration but wider. they usually go together of course, more lift and longer duration.
big lift does tend to batter lifters a bit, as well as the springs.