The primary purpose of a tactical vest is to carry extra mags. If you're using Hicaps you're short-circuiting that, so you could pretty much play in just a tshirt with a 1L canteen on your belt.
Of course, its a different kind of play as virtually all milsims and many other games will either not allow hicaps or frown upon them (for example the game in Drummondville this past weekend, which was real-cap loads only). Then again, you're talking about "being good for a complete round" which sounds like a skirmish, so I wouldn't worry about a tac vest unless its just for looks.
When you're out in the woods for a full day with only the stuff you're carrying on your person, your needs in terms of gear become a lot clearer.