If it was an option there is no way I would not get the di2 on a time trial bike. I am running SRAM on mine, it works well but it does not compare to electric. Also, with the amount of money you are planning on spending attempt to negotiate a full professional bike fit with purchase.
If it were me I would go with the di2 with power meter. You can alway get a disc cover from
www.wheelbuilder.com to hold you over until you can purchase some nice wheels.