Kirk, nice job on the suspended ceiling. I remember talking about this with you a while back and was wondering how it went. I'm glad it's working out well.
RE, if the 1048 was going to be your production oven, then there would be no question what I'd say, but since it's just for testing, I wouldn't go crazy with the suspended ceiling.
When you go into production, you're most likely going to need to do some major tweaking to the recipe when you scale it up, so adjusting for a shorter bake at the same time shouldn't be the end of the world. Going from 6ish to 4 may not take many changes, if any.
In the mean time... you could crank the oven high and play around with some materials that will handicap the heat transfer on the bottom.
Cheap Walmart Stone
If you go with the splits, I'd increase the pre-heat time at least an hour.
The most important thing you can do right now is
zero in on a final flour choice (which I think you're doing)
stretch as many skins as you possible can (the thinner the better)
start building up as much data as you can regarding fermentation temps/times.
The last one is critical. You should have a book with temperatures of every ingredient and setting (and other data such as flour age and yeast age), with the time for each setting and the time it took for that specific formula to be ready. You can't have too much experience predicting yeast activity. You need to develop a same day, a 1 day, a 2 day and a 3 day dough, along with varying lengths of bulk. In addition, you want some practice with both room temps (at different temps) and cold ferments. You'll want to have data on a variety of formulas to see how modifications, such as more or less water, impact the fermentation time. You may not have every possible permutation in your book by the time you begin, but, you should have enough data to extrapolate a multitude of different scenarios.
For instance, let's say your flour shipment is late and you end up having to use it right off the truck and it's 10 degrees cooler outside than the temp you normally store flour. You need to be able to adjust your water temp or adjust your yeast quantity to hit the target time the dough needs to be ready. Or let's say your flour is really late, and instead of being able to do your normal 2 day ferment, the dough has to be ready the next day. You need to be able to be completely confident that the quantity of yeast you're adding will give you a dough that will be ready exactly when you need it. The more data you have collected, the easier it is to handled unexpected scenarios. The worst thing that can happen is that something happens that forces you to change your process in some way and the changed parameter is one that you've never experimented with before and you're flying blind.