>>>>>There are quality commuter bikes like the Brompton and Birdy, but most others are fairly low performance, cheaply built machines<<<<
At your weight class, I would stay away from Brompton, Birdy or any 16' wheel folder. In my opinion, you need to look at Bike Friday since they offer the most support for their product than any of the other brands in the U.S. BikeFriday will buid a bike to meet YOUR needs instead of the other way around. These are NOT commuter bikes but serious traveling bikes. This is a big difference since a commuter bike tends to be under geared or low quality which is not what BikeFriday is about. These bikes are not cheap by any standards but your're getting 21 or 27 speeds compared to a 3 speed Brompton.
I also recommend the Montague MX ($595.00). The only problem with this bike is your not getting the support you would from BikeFriday.