Macclesfield is a very tight and twisty track, the straight is half as long as what an average off-road track has when you consider Worksop, Bury, York, Broxtowe, or pretty much any other circuit.
Granted, top speed of your friends buggy is going to be quicker. Get him on a circuit and it'll be thermalled in 3 minutes, and before it thermals it'll either broken or on its roof more than its wheels...... that motor is just far to quick.
For Bury, your setup will be ideal. The leading cars at Bury are likely to be only using 6.5 motors or slower, especially with Lipo.
For Macclesfield, what you have may also be too quick - you may need a 7.5 or 8.5!! Honestly, lap times come from doing clean consistent laps, and if you can't do that due to the speed then you need to be slower. Slower is faster
