I did some testing with a 4250 size 350kv and it struggled to restart the pump above 15 bar. I have seen on some German forums reference to a 5065 size motor being used instead of a 4250 size. Here is one:
http://www.hobbyking.com/hobbyking/s...dProduct=18176
Some 4130 motors (this number is not the outside motor size and is similar in size to a 5065) would probably also work. The best option is a Torcman motor but these are very expensive and hard to get.
You could also use a 4240/4250 size with a 3:1 planetary (from a cordless drill).