I have been using Dillon presses since 85'
A few things:
*Brian Enos has not sold Dillon presses for a few yrs now.
*Get on the Brian Enos forum and ask the question and do your research there. Most of us shoot high vol and compete. There is no group of people more experienced on dillon presses outside Dillon's own techs.
*Be sure you give them the total number of cartridges you plan now and future to load for. Also very critical how many rounds between switch calibers and how many rds per yr of each for total vol.
Tech, Usage, Troubleshooting...
forums.brianenos.com
*As I understand it, your volume will be a few hundred rounds per session per cartridge. Say 300-400 of each caliber? 9mm, 45acp, and 5.56. How many rds of each do you plan to go thru per year? 400, 1000, 2000?
*Who here is still thinking a 1050/1100 level machine is a good recommendation for this kind of volume!?! I SURELY DON'T
One advantage to the 550C is cartridge size. Another 2 are utter simplicity and rock solid reliability with little to no tinkering to work well. Cost also. It can load from the tiny 32w sizes all the way thru the lapua mag and weatherby cases. It's manual indexing. The only upgrade I ever really did was adapted a hornady lnl bench rest version powder measure which did wonders for throw variation and allowed Lyman-M type expanders. Also got rid of that dillon fail safe road contraption.
What the XL750 gets you is more automation. Case feeder and bullet feeder options $$$ and of course auto indexing. But not the HUGE cost increase for caliber conversions and time of the 1050/1100 models. But you do have to tweak these 650/750 presses to get the best out of them. There were a number that are nice.
Based on your level of loading there is no way you would want to be using and pay for a 1050/1100 press. You could get a fully decked out 550 quick change sets dies etc just for the cost of the conversions for the 1050.
You would be happy with a 750. It would give room to grow if you are confident that will be the case. But there is a bit more tweaking for the auto indexing smoothness but that may have been addressed in the 750. More complex. But likely the most used by 3 gunners and other lower vol competitors
The best way to do 5.56 is setup two plates one for case prep and one for loading and do a 2 stage run thru.
My current ideal would be a 1050/1100 for 5.56 and another dedicated for 9mm. With a CP2k for case prep. 550 for 308 and load dev on all high vol cartridges. I use inline hand dies for all my precision stuff.
No way I pay for a 1050 if my vol was underr 10k/cal yr
Imo you NEED a 550c but you may want/desire a XL750. Just when looking at prices do not forget all those accessories and conversion parts and dies. It adds up very quickly.
BTW you can adapt the hornady powder measure to the 750 but it may not fit if you add case feeder.