This is Most asked question. Believe or not, it was asked from limo company's employee and other drivers too.
Please let me give you more information than just numbers. Stretch limousines are semi-custom made and every limo are different design and layout. Many limousine companies call as 6 passengers limo, 8 passengers limo and 10 passengers limo in price list. But it doesn't work that way. We as professional limo chauffeurs and limo builders call 72", 100" or 120" limos. Some builder makes 85" and 130" too. It also same to Stretched hummer and stretched Escalade. 160" Hummer, 200" Hummer....many different sizes with different layouts.
It all depends on how big/small you are, what will you dress and how do you want to be in limo. If you don't want to mess your wedding gown or tuxedo, don't try to max load to limo. If you don't care your elbows and knees touching to your friend or family because you maybe get drunk and spill your beer anyway, you maybe try to max in.
Stretch limos are just like suite room in hotel. Choosing size is not only because number of people. Sometimes size is for Luxury and Comfortableness. Many of my clients sleep in limo comfortably when they go back to home at end of night. and some of clients get drunk and crush to floor holding somebody's shoe and leg. It's up to how you want to make your night/day. I reccomend you to subtract 2 from max passenger. Just like 4 passengers sedan (Factory Lincoln or Cadillac) are designed for 2 passengers on back. If it shows 8 passengers limo, think it as 6 passengers limo and if it's shows 6 passengers limo, think it 4 passengers limo.
Reminder for Airport trip, Very important
Please remember Stretch limousine's trunk is same size as Sedan. Actually its capacity is smaller than sedan because we usually carry cleaning kit, Ice, extra drinks,etc in trunk. I put my full size spare tire in front passenger area but some Limo carry it in trunk. (Town car carry only small tiny temporally spare but it won't hold big heavy limo when we need it) You might think "We order 9 passenger limo for just 6 of us. it's big enough". Yes it's enough to "people" but not for your bags. Most of Lincoln (Sedan or Stretch) can hold 3 full size suitcases and 2 soft bags but not 5 suitcases.
When I use to work for large limo company, it happened almost every week. When I met passengers at Airport or Hotel, 7 suitcases, 3 soft bags and 2 carry-on bags followed by passengers. There is no-way to put them all in trunk and no limo have roof carrier like tour van. We have to find 2nd car to put all bags. We can put some of your bag inside of limo but please remember that you will have full responsibility for inside of limo if it make damage.
Please re-evaluate volume of your luggage before choose your vehicle. If you don't think your luggage won't fit to your own vehicle, most likely it may not fit to my limo either.
Usually, 72" Lincoln stretch (so call 6 passengers limo) are face to face layout. It's a 6 feet stretched from original Lincoln. Factory original seat on original position and slightly narrower seat facing backward behind of partition . Depend on how big you are but you can imagine how uncomfortable for someone who sit on middle, if you use it as 6 passengers. I should say 72" Lincoln is comfortable for 4, maximum 6.
6 passenger limo
6 passenger limo
100” Lincoln are called 8 passengers limo. It’s a 2 feet and 4 inches longer than 72” Lincoln.
It has about 2 feet small seat on side. 6 people comfortable 8 max.
8 passenger limo
8 passenger Limo
120" Lincoln and Chrysler are usually J shape seat. Because it's a J-Seat, you can squeeze and push each other or you can sit as way to not mess with your dress. I should say 7 comfortable and 9 max. but remember, if 9 of you sit on 120" limo, your elbow might hit somebody's chest and somebody's knee might hit yours. 5th door (middle door) is getting popular for 120" limo but not on all 120".