Surface Pro 4 4 gig/128 i5 or 16 gig/256 i7?

[Windows Central Question]

I've got both Surface Pro 4s. Has anyone here tried these two side by side? I was having some lag with the 4 gig (i5) so I got the 16 gig (i7). the 4 gig got hung up on validating my copy of MS office. The problem I'm having is the 4 gig i5 is $850 plus tax. The 16 gig was $1600 plus tax. I got at Costco so they both came with the pen and keyboard. Is the 16 gig worth the extra $750 even in spite of the Pro 5 coming out within the next 6 months or whenever they get around to it?