magnepanLRS or 1.7i ?

Your amp has enough power (300 watts/ch @ 4 ohms).  People will argue about if the amp is high quality enough, something only you can decide.  Larger Maggies allow higher sound pressure levels and have more bass.  Smaller maggies with a sub or two have a fuller range and more bass capability.  You need to establish the factors most important to you and pick which fits your needs best.  

You can literally buy 3 pairs of the LRS for the price of one pair of 1.7i.

I say go with the 1.7i and save yourself from upgrading later.
You'll get better frequency response and bigger better sound.

If you have the space, it makes sense to go with the larger Maggies.
The new LRS will definitely need some subs. The larger Maggie would benefit from a sub or two, as well, like the Vandy 2wq, which has the benefit of relieving the amp from the heavy demands of the lower frequencies.
Though I haven't heard them, Ralph Karsten swears by Sound Lab speakers.
Bob