So, I’ve always used an 1100 wt model, and never had any problems keeping my temps up, even though we do our SV’s in garage, where in the Winter, it commonly gets down in the 40F’s. I use a 12 qt Rubbermaid container, with insulating sleeve, and silicone cover.
I’ve considered the 900 wt Nano, but concerned about it being able to maintain temps in a 40F garage ? I’m thinking it could probably do it, but it might have to work pretty hard to do it.
Do you think Id be okay ? Maybe it would be worth increasing the insulation in the Winter ? I could totally construct a 2" Styrofoam box, to perfectly fit my Rubber made, leaving the neoprene cover on it to. (we have tons of 2" Styrofoam that comes as packing with some of my GF’s orders. We try to reuse it, because that stuff kind of sucks in the landfill)
I think if you start with water that is very near your cooking temperature either unit will work fine. Adding insulation to a cover will reduce one of the big areas of heat loss. Heating cold water and using a very large volume container are where increased wattage helps the most.
The Nano will be just fine as long as you are using an appropriate amount of water and/or add some insulation
Thank you 
Firstly, for us Europeans the Original Poster is referring to 4.4 celcius / 40f.
We have no idea as to the insulation of the container but at around 12 litres its a small cooler atypically with a low grade expanding foam as its insulation (always good to know the U values in relation to efficiency) or simply an extruded polystyrene, which isn’t great but better than nothing.
A Silicone cover which presumably has a tight condensate leak proof cut out will under normal conditions with pre-existing water at room temperature speed up heating times (& therefore assist temperature stability) by around 30% & radically slow cool down …in a instantpot type s/steel inner on your worktop.
Whilst the OP does have lots of extruded polystyrene the U value is low compared to an equivalent thickness PIR foam foil board, & sides made as tight to the shape of the container as possible, compete that with a lid of the same construction (& all cut ends taped with aluminium foil tape then you will be laughing OP.
If you want to to take it a step further a big oblong cooler like I have with the original Anova unit & surround constructed in the same manner will work for those big ribs & large meat slabs (if you have a capable enough vacuum sealer)
Lids & bases are essential to fit as ifyour container sits on the floor likely it is on an uninsulated concrete slab (drawing lots of heat away) if on a raised table less so, unless its maybe metal in which case same draw of heat into the metal, so slab insulation is always a good thing to have & is easy to cut.
If you want to reduce the energy outlay then ANY decent thickness of insulation ALL ROUND will help stabilise temperature & therefore heat cycling, if you miss any side off then obviously that is the escape route (losses) make any lid as good as the sides.
U value of a typical generic slab of 50mm (my minimum) to add decent insulation value assistance, though my ideal is around 120mm all round for somewhere that gets as cold as your garage, …the thicker the better really. (a decent PIR foil foam sandwich is around 1.74x the thermal property of the same thickness of plain old glass fibre insulation for a simple comparison.
Your garage gets cold, & likely too hot, in essence this is why folk retro fit (& tape seal) walls & roof undersides to make for a more comfortable useable space, any walls adjoining your garage would seriously help if they had this type of insulation to control heat / cooling comfort & expenditure.
To go the other way & offer you another “extreme” example we placed a 120mm slab to the side of our woodburning stove (efficiently burnt one) it deflected around a third more heat back into the room! (usually lost to the immediate outside wall)