I²C with ATTiny85 at 8MHz using TinyWireM library
You really just need to scope the signals, even if it's with a DSO Nano-type scope.

Without downloading the datasheets:


I would guess your pull-up is probably too small, but possibly too large (scope it)
Slew rate may be either insufficient or too steep (scope it)
Be aware that the ATTiny runs at "8MHz", and not 8.00MHz. The timing error can be off enough to cause communication issues at high speeds while working well at lower speeds (scope it, and/or start at default and incrementally increase speed by 0.5MHz until it stops working)
MMA may not support a typical protocol feature being used, i.e. 'repeated start', burst transfers, etc. (datasheet register/programming section)


Edit: Both the ATTiny and the MMA should have bypass capacitors near the power pins.