I think we're averaging around 5-6 fights per 5 hour session in my 4e sandbox game.

Lemme see, last session had:

Fight with Ettin, immediately followed by
Fight with Ettin's big brother
Fight with Ankheg
Fight with Vine Horror
Encounter & flee from Roper
Fight with 3 Ankhegs (which killed 1 PC).

Previous session had:

Fight with 3 Dire Wolves
Fight with Fey Panther
Fight with 6 Orc Warriors
Fight (shooting at) Orc Warrior & Hobgoblin Archer
Encounter and flee from dozens of Orc Warriors
Fight with 2 fire beetles

Quote from: Elliot Wilen;331830Even if it's not a dungeon crawl, combat has a way of clarifying the situation to set up the next non-tactical decision(s) by GM and players.

This mirrors our experience as well.  The easier and faster the fight system is the more we are likely to use it.  So if you look at a session there still may be 2hrs spend fighting, but broken up over several smaller fights.  So you may follow a pattern of story, fight, story, fight, story fight.  Where as in a more complicated and drawn out system it usually just goes story, fight.

So I much prefer the former.  It seems pointless to me to build a session around just throwing in one fight because you don't have time to do anything else.

Most of combat is choosing not to run away.  Except in rare circumstances, players do not need to engage in combat in as much the same way as they do not need to engage in any aspect of the game.  The fact that you and your players pursue combat as regularly regardless of edition is notable.  As is how much longer individual encounters last in progressively later editions of D&D.  

What I'd point out is how much more exploration of the map it is possible to accomplish in previous editions rather than later ones, if combat seeking is constant.  And, if engaging in noncombat elements of the game is either important or irrelevant to your players, than your group's preferences should become clear. They will either gripe the combat encounters are taking too long or aren't detailed, varied, and/or long enough.

So much depends on the players.

If you have people who know their characters and their abilities and the system, then even Rifts combat moves swiftly.

If you have a couple of gamers who never pay attention to the rulebook, and never remember which dice to use, then combat will take longer.

I personally LOVE combat scenes so I revel in details and the excitement.  So if a fight takes 1 hour or a major fight takes 2 hours, I'm cool with that.

In my D20 game (Legion, running with Star Wars D20 Revised) I usually handle 1-3 combats per session.
In my RIFTS game its usually 1-2, but our sessions are shorter.
In Amber and Pendragon its totally variable.

Back when we were playing the epic RC D&D campaign, it was easy to do a metric fuckton of combats in a single given session.

RPGPundit

My ideal session has probably 3 separate fights taking about 10-15 minutes each, about 90 minutes of exploration and problem-solving (including running away from, sneaking past, or tricking your way past several more potential fights), 15-30 minutes of in-character playacting (likely including talking or bluffing your way past at least one potential fight), and 15-30 of miscellaneous joking around and off-topic banter, for a total of about 3 hours of play, plus another half hour pre-game and a half hour post-game for socializing, kibbitzing, and bookkeeping. If combat takes up more than about 25% of the total session (either because there are a ton of separate fights or because each fight takes a long time to resolve) I get bored.

In our recently concluded 4E game, a fight would typically take 3 hours to run.  That's pretty much been the case since we hit the paragon levels.