If you join Marriott Rewards and link you accounts you can instantly transfer points from your SPG account. Simple. 200k SPG points will equal 600k MR points. With Marriott, you get the fifth night free so staying four nights leaves a free night unclaimed. Also, since you have enough points, getting two rooms and asking the hotel that they be next to each other may be a better option because you can do that with points and no cash.

Finally, being disappointed with a lack of choices? Paris is the most requested redemption. August is a busy time for family travel. We are only three months away when most families would have made these plans months ago. There are few family rooms and they fill up quickly. You should be glad there are any rooms, let alone several Marriott choices, then expect when you make late plans the most popular redemptions aren't all sitting empty waiting for you.