he is doing a serious commercial game ?
does it have a real team or does it have a real solid concept/art/ideas perhaps ?
in that case he could consider Torque for terrains caus it has all tools needed , very fast optimized grass generator (with wind taked account)
and more important : Lightmapping.

i just talk about that caus it seems a real solution for someone wanting to go fast and not spend lot of time with tools or missing things.

my bad talking like always