Which heats quicker High or Low speed pumping

[JohnT]

So High flow will heat faster but increase electrical cost since the pump costs more. I have to decide the if the trade-off is worth it.

Will it heat 10% faster 50% .. 80% Any guesses ?

The only advantage of the low flow would be less per hour pump cost. Assuming the pump's electrical use is in direct proportion to its flow, the high flow would win hands down because it is more efficient and the total amount of heat needing to be added is the same.