A couple of years ago, it would have been a simple matter of weighing up costs and turnover target(s), in that one would cost more than the other, and one may be better suited in terms of sales volume (eg one off items, available for a limited time at auction has a higher sense of urgency if someone wants to secure it than a 30-day BIN, even if there's only one available), but these days auctions don't quite have that same sense - I know you're not speaking specifically about using auctions, but it would probably be the major benefit of not subscribing to a store, because clothing auctions would then cost you $1.50 a pop.

Visibility.... well, new listings get a temporary boost, so 3 x 10-day listings vs 1 perpetual listing might work out if you can't build a listing's standings in other ways (i.e. sales history being the main way, which you can't do if you only have one). 

On the flip side, I suspect there's differing impressions from the buyer's perspective to see a listing end and relist continually as opposed to an always-available listing (a subconscious thought of, didn't sell, didn't sell again, and again... vs it's still available, if you know what I mean?). That's presuming a buyer sees this, anyway, most of the time they're probably not going to look at the number of times an item has been listed etc, but it may be something to think about. 

Personally, with 300 items, I'd probably go for the store, since it would be impossible to offer them all month after month without one. 40 free listings, with free relists = 40 items for up to 40 days, leaving 260. Most offers are for 150 items, 10 day max (not sure if they get free relists, but if not, you'll need another 600+ listings each month to make them always available, the cost of which would be $900 without a store, $120 with, and a 0.04% saving on FVF to boot (lucky you!), but no auctions... and also no hoping for free bonuses, less admin in working out what does and doesn't need to be relisted, and so on. Especially if it were going to be over a total of 3 accounts.