Hi everybody!
Sorry if I'm necroing this post... just wanted to add my 2 cents and confirm that things don't work well at 250k baud.
I too have been working on bypassing the Bridge library which (in my experience) is VERY slow. With regards to the baud rate, I agree that 250k baud seems awfully high. I also had trouble with dropped characters at that rate when reading them on the device. What if it's purely a matter of CPU Speed? At a rate like 250k baud, the CPU shouldn't have much time to empty the UART buffers before they overflow. Might the dropped characters just be lost in a buffer overflow because the CPU cant quite keep up?
Anyways, I disabled the tty and connected at 115k. It works great 
violinuxer