I am currently on my Lagoon 42, Sea Tiger. which is also in TMM fleet.

In regards to space, Lagoon 450 does have somewhat more space. With 5, you will have plenty of space on the 42,

Speed is determined partially by length and the L450 is going to be faster by about 1 knot of so.

Self Tacking Jib is really nice when I am doing most of the sailing de facto single handedly.

Look for extras: A few boats in TMM have Watermakers... Very nice feature as we are 10 days into our trip and have not docked ANY for water... And crew is not in the water conserving mindset. (Having to stop for water can affect itinerary, as well as delaying for dock to open or waiting for others to leave dock. Just a couple of weeks ago, North Sound was without water, thus severely affecting those planning to sail to Anegada and needing a top off.)

Sea Tiger has 4 bean bag chairs which makes for great seats anywhere on the boat. Much better than factory cushions. (Our professional delivery captain loved them !).

Also Sea Tiger underwater lights as well as brackets for 2 Stand-Up Paddle boards, making them easier to stow and also out of the way of the deck.

And yes, TMM maintenance on the boats makes them the hands down choice.

One "draw back" of the Owner's Version(3 cabin) is that the owner's hull is so disproportionately bigger than either other stateroom, then the other guests may resent it. Just have a upfront method to dealing with this issue: Upon organizing trip "cabin assignment in order of commitment to trip (ie deposit received)" or lottery.

With your crew size, pick between the 42 and the 45, but note the extras.... especially Watermaker.