Save for a B6D or a new ESC?

[oldschooldriver]

I'm looking for some advice. Currently using a cheapie Trackstar 120A Turbo v1 ESC in my B5m lite. Not sure what I should be looking to invest in next if it should be change to a B6D or change the ESC. The existing car handles pretty well and seems fairly quick with a Reedy 6.5T. Im getting there with my driving. What should I look to do next - new car or ESC?

I drive a mixture of indoor mixed surface and outdoor. Im looking to gain an extra second a lap between both my driving and equipment upgrade. What gains do you think would be possible with car or esc change? Any advice or recommendations gladly received.