I always thought it would be a sensible option for your first FAC application if you could specify a sensible range of calibres, or something like 'deer legal, calibre TBC'. When I applied I had previously shot .243, .308 and 6.5x55 and would have been happy with any of them. But to be honest funds were limited and the determining factor was always going to be what turned up as a good deal on Gun Trader! Having to make a choice I plumped for .308 and then waited for a good deal on a T3 but I could just have easily have picked up a .243 or 6.5x55 if I hadn't had to commit to one or the other up front. Besides giving those with limited budgets more flexibility it would also allow the purchaser to prioritise the things like fit and suitability that are getting highlighted here and are probably much more important than an arbitrary calibre choice.
This would be far too open, you could jump straight on to an HME calibre like 300 win mag or even .338 Lap Mag or .50 BMG if that was what the slot was for, then you would have to start adding up to .30 Cal and 3000 ft-lb muzzle energy and that sort of thing, would all start getting a bit complicated. The fit argument doesn't really stand up as most rifles will be available in all of the common calibres so you can get a t3 in .243 or .308 or 6.5x55 and economics can't come into it as you can't request say 5000 rds of 0.22 because you can buy them more cheaply, it doesn't constitute good reason.
At the end of the day .243 up to .308 will all stop deer with correct shot placement, if the OP has the opportunity to try different calibres / rifles great, if not shoulder a few at the RFD, pick a calibre and job done.

but I agree and I am biased, 7x57, 7/08, would be my suggestion. Both are superb and if perchance the hunting distance increased both will suffice.