I have spoken with Mike on many occasions. His coils , burners and systems are impressive. The 11gpm at 4000psi is also the machine I looked at, actually I upgraded the spec to 12gpm and lowered the pressure a bit and increase the HP.
His Phoenix propane burner is patented, no moving parts, lowest amps draw of any burner, and can be tuned easily in the field to adjust output.
You could talk with Al Patterson, a member on here who has them, do some research, sight the pros and cons of propane and see what best fits your needs. (Silver Eagle also has diesel burners, Beckett)
I also looked at the manufactures of the machine you currently own, all great too.
After all my research I went with diesel burner from a semi-custom manufacturer.
If you have more questions, "shoot"