This is a good comparison (£350 beater vs £12K superbike).
Both riders “felt” much faster on the expensive bike and it was between 1.5 and 3% faster over a short, flat race course. So around 5-10 seconds faster over a 5 min lap. This was at an average speed of around 42 kph, so relatively fast where aero gains would be significant.
it’s worth watching the video as it highlights how you can achieve most of the performance gains without spending anything like £12k. Start with tyres and clothing fit etc. Bikes are the ultimate in diminishing returns for cost.