I'm interested to see what you find with this.
I have Xray XB8s in both BL and Nitro also. (actually 3 of them, 1 nitro, 1 bl with conventional motor brake setup and, 1 with BL and mechanical brakes and a TeknoRc clutch setup.)
What I found was I was faster with the BL, but I atribute alot of it to my driving style. I have always been an electric guy and tend to try and drive with the smoother throttle style that goes with electric. This doesnt really lend itself to being fast with the nitros. From what I see, typically the fast nitro guys are very harsh with the throttle, almost like an on off switch. They are either full throttle or none at all. I just cant get used to driving like that, so I find myself to be more sucessful getting round the track clean and as fast as I can with the BL. Like you I prefer the mechanical brakes on the BL though. So soon I will be braking down the 2 BL XB8s and taking the Mechanical brakes from the clutched version and putiing it on the conventional pinion drive buggy and making what I think will be the best setup for my preferences.
Please do update this once you have driven them back to back. I actually find that it takes me 5-10 minutes of driving to actually get the mental adjustment down when going from nitro to BL or Bl to nitro on the track.
Please take all of this with a grain of salt folks. I am by no means what I would consider a fast/good driver. Not an even an a-main guy at the local track. (But getting better all the time
) This is all my opinion and what fits my driving style.