Sorry, but that's just silly! What the h5ll have you got in your calendar to make it over 2GB? My pst files used to get larger than that (the email pst, not the calendar) but now I make sure I keep the amount of data small - mainly through not keeping attachments with my email.
The only reason you need a different calendar app on the phone is if you don't like the way the stock one works. The greater majority of the calendar apps out there use the same storage as the stock calendar, just display it differently.
Which is why I'm asking for a calendar app that doesn't use the built in sync system.
I have calendar data going back to the 80's when I had my high school schedule on a commodore 64. Its been imported and converted many time over the years to various programs and added to. when I was contracting I had to keep track of my hours spent at thwe client sites and what work I did.
I beleive I shouldn't have to open multiple programs to complete a task. It seems silly to me to open a calendar to see when my appointment is, then open a note taking program to take notes about the work I did then open a word processor to create the client billing sheet then open a spreadsheet to type in the billable time. I had a nice system where everything couple auto generate off the calendar entry so I could use my Windows CE 2.0 PDA and just enter calendar entries while at the client site. I would just tag a category as to weather it was billable or not and if it was buillable to the manufacturers warranty or to the clients helpdesk or networking services then some code and macros would generate the rest of the documentation once I sync'ed. The file explorer plugin for outlook 98 was pretty helpful because I could point to documents from there.
Then the stupid iphone came out and got popular and everyone elses interface had to be dumbed down because the iphone is what sold. Its now over a decade later and I don't yet have the same simple functionality as I did in the late 90's.
But getting back off my rant for a minute, over the years I have amassed hundreds if not thousands of files but the calendar is the reference that ties them all together. So that has become my most important file. If I need an example to demonstrate to a client why its important to regularly patch their servers I can go back and find several incidents over the years just with a quick search. I was filling out a background check form last week and needed to know the dates I lived at each address. Those are in my calendar but the phone won't sync or search that far back and its not really an issue of file size. I've taken the .ics and copied it over and can search with a text editor so I just need a calendar app that will directly read and write .ics files. I can then setup my own sync system and just cync the files back and forth.
Those yeas of .ics files are no where near 2G, MSOutlook just wasn't efficient as storage, one of the many reasons I had to drop it.
FWIW I've never been completely happy with any PIM/calendar I've used. I think the main issue comes from all trying to emulate the paper day planner. IMHO I shouldn't have to have tasks, calendar and journal in separate views. So when I would get up in the morning I had to check multiple views to see everything. A lot of programs have tried to work around that with a today pane but really just view everything in one place. Some calendar programs will let you view tasks on the calendar which is a start. MS Outlook would also never impement any kind of project managemt since they wants you to buy MS project.
The best PIM/calendar I have used so far is KDEPIM/Korganizer. It will let you have tasks and subtasks which is sufficient for simple project management. I did manage a one way sync to my phone by using a icaldeamon to sync the files up to google. Then if you delete the google calendar and resync once every coupld months it sees everything as a new entry and therefor sends down to the phone but you have to put your phone aside for a hour
Borrowed an ipad one time and tried to get it to see everything and it never recovered.