If I were you, I would go with the 1.5Y. Y winds are a tiny bit more efficient than D winds and you can play with the timing on Y winds, while its always best to keep it at zero degrees with D wind motors. So the extra rpm of the 1.5Y shouldn't be a problem.
An even better setup would be a 2Y with a 6s pack that fits underneath the body.
Check out my custom converted 8ight:
Sub 7lb, lowest CG of any 1/8 buggy