[xQx]

I've been swapping between E25 with the JB4 on BMS Race BEF and the MHD E25 OTS tune. With a FBO N54, I found the MHD tune had noticeable low-down pull that the JB4 maps don't. The MHD tune targets higher boost than the JB4, and didn't pull timing as quickly as the JB4.

After installing inlets+outlets, I found Map5 in the Jb4 with the race BEF to be much smoother than the MHD. That said, the outright performance of the MHD map was better (again, thanks to it targeting higher boost and pulling timing less, though the fear here is that the only way you get that is by being less sensitive to knock).

I did a heap of 3rd gear runs with each tune, and have attached my best virtual dyno of both.

In the end, I've dropped back to pump gas and JB4 map 2, because over my time playing with E25 - E40 I've found the limits of both my HPFP and LPFP.

Long story short - from everything I've read, it's one or the other; your Backend-flash options are:
1) JB4 in gauges only mode (4/4) with MHD E25 Map (E25)
2) JB4 in BEF mode (4/2) with BMS RACE BEF (E25)
3) Custom tune (either with our without the JB4)

All that said - if you do have the JB4 in gauges only mode, I found it would still drop to Map 4 if it detects a failsafe condition. (Of course, when you're in Gauges only 4/4, it doesn't make any difference to your tune what map the JB4 is in, as long as it's not zero). - So, if you stack your JB4 in gauges only mode and keep the gauges on the dash, you still get a small safety that people with no JB4 do -> Keep it on Map 5, and if you ever see it drop to Map 4, slow down and examine the logs to find out what's triggered it.