More upside: Two-flat rental or sfh with big downpayment

[Luke Schmitt]

First time poster, can't wait to tap into all of your insight. I own a two flat (purchased for $400K in 04/15) which was completely updated in 2013 in 60618 Chicago. I have a 30-yr fha fixed mortgage at 3.5%, with PMI of $256 and monthly payment of $2,595. I owe $365K on the mortgage. We live in the top unit which is 4bd 2bth, nice finishes, all wood floors, nice deck, small backyard, two car garage. Our ground level unit is a 2bd 1bth with storage room and adjacent shared laundry in rear of ground floor. We rent this unit for $1,250/Mo. Our realtor looked at comps and believes our house will assess for $480-$490K and would list at $499. He also said we could conservatively collect $2,000/Mo for our unit, but quite possible to be in $2,300/Mo range. We would like to purchase a SFH in the area and my question is this: In the long run, what would be more financially wise, holding onto our current property and scraping together a small downpayment for a less expensive SFH or selling our current property and applying a $100,000 downpayment toward a larger SFH? 60618 seems to be a very stable and appreciating market for mid to higher end homes. Thank you!