they are very different cars and they handle very differently, but I'll be honest. I was faster with the Mugen. The mugen is easier to drive in my opinion. Now, the mugen does have very week front lower arms, and I was breaking them at least twice a month, that was what push me to the D815. the D815 is super durable. But now with the release of the Xray 2016, you can put Xray arms in the MBX7R and they will not break. I still have my MBX7R-Eco, I changed the arms to Xray arms and is awesome. I'm the same way here, only guy in the track with a HB and is hard to get parts. I'm waiting on the MBX8 to come out and I will sell the D815

I would go for the hot racing c hubs, and maybe the king headz spindles and rear hubs..:-) the orange hexes are for the trophy truck, got it on ebay
http://www.ebay.com/itm/NEW-Org-Blki...item4d1be79597

I also have d812 diffs, light weight parts,rear shocks, an modified rear hubs.
great truck, its almost as perfect as i want;-)