In all but a few cases, "pay with miles" is not an efficient way to use miles. You could probably get a full Skymiles award ticket (maybe even a BE ticket) for less than the 150,000 miles you're looking to spend through Pay With Miles. And I haven't seen any true blackout dates with Skymiles. I've seen certain time periods with no "low tier awards" but you should always be able to get a mid or high level award. Although it may be different for flights on KLM.

However just to compare value, you can get a J Award to Australia for 150,000 miles, and J tickets to Australia can be $5-10K. Much better return on investment than spending those miles through Pay With Miles on a $1500 ticket.

PS: Once you use any amount of Pay with Miles, your ticket no longer accumulates any miles (redeemable miles or MQMs).