1) Assuming a group of 6 characters and an equal number of baddies, how long in real time does one IP from each participant take?
Well, I look at it as "what's the fastest an individual can react" because a character could delay so how long does their one IP take...as long as they want. But from the other side, what's the quickest a person can react...which is interestingly "just faster than the fastest person involved." Meaning, if a character with 1 IP wins initiative vs a "faster" character with 4 IPs (rare, but can happen), then that means, for that Combat Turn, the 1-IP character is acting (can act) within the first 0.75 seconds of the 3 second long Combat Turn...however, that 1-IP character's reflexes are so slow (compared to the 4-IP character) that it will take the 1-IP character 2.25 seconds to be able to react to the four actions taken by the 4-IP character.
If the 1-IP character delays or rolls poorly for initiative (well, "average" against a 4-IP type opponent), thereby acting last in the first Combat Turn and then beats the 4-IP character in the following Combat Turn (meaning in the first Combat Turn the 1-IP character acts after 2.25 seconds, and then acts again between 0.75 to 1.5 seconds later...which is a faster reaction than they are normally able to attain) I "flavor text" that as either luck, extra twitch in that moment, had a chance to notice something extra, etc.
Because a Combat Turn is defined as 3 seconds long, then characters are constrained by that time. It's not that a 1-IP character takes 3 seconds to perform one action, it's that it's a combination of it takes them x seconds to perform an action and y seconds to send/receive the signals to and from their brain to set up for the next action they want to take...and that for the 1-IP character, x+y generally equals 3 seconds.
However, because in the physical world Initiative Passes are capped at 4 (5 from War! ?, but the idea is the same so I'll stick with the 4-IP cap...just change the math if it's now 5-IP cap in the meat world), and the 1-IP character will be acting in the first pass along with the 1st action of higher IP characters, it means that the 1-IP character can, and will, act within 0.75 seconds (0.6 seconds if 5-IP).
From the sound of it, you're more concerned with the "x," the length of time it takes to perform the action...because while all characters, from the 1-IP to the 4-IP are acting, in the first pass, within 0.75 seconds...their individual actions are not all temporally equal. This is where I just apply a nice arbitrary "it doesn't really matter" attitude and decide just that a complex action will take no more time than 3 seconds divided by the product of the highest IP-character's IPs and the number of participants. So if there are 2 characters each with 1 IP, then any complex action they take will take no more than 1.5 seconds. If there are 12 characters, with the highest IP at 4, then any individual complex action taken will not take more than 0.0625 seconds. Yet this time minimum can be increased because if two people tie then they are acting at the same time. So if 2 of those 12 people tie with each other, and 3 others tie with each other, then there are only 9 unique turns in the first pass, so any individual complex action taken will not take more than 0.083 seconds. One could also choose to simply divide 3 seconds by the total number of initiate passes of all the individuals involved (the previous example acts as if all participants have the same number of IPs, all at the highest value of those participating individuals) which would "embiggen" that time interval a bit more.
House RuleOnce my players get proficient with the overall rules, I plan on staggering IPs during a Combat Turn. So that things become more "evenly" spaced to reflect "reaction time." All characters, regardless of IPs, will act on the 1st pass. However, if there is a 3-IP character, a 2-IP character, and a 1-IP character then they will act on the following passes;
| Pass-1 | Pass-2 | Pass-3 |
IP-1 | X | - | - |
IP-2 | X | - | X |
IP-3 | X | X | X |
And with a 4-IP character involved;
| Pass-1 | Pass-2 | Pass-3 | Pass-4 |
IP-1 | X | - | - | - |
IP-2 | X | - | X | - |
IP-3 | X | X | - | X |
IP-4 | X | X | X | X |
/House Rule2) Without trying to revise the IP system, has anyone come up with a good way of streamlining the OOC time for combat?
Other than kicking my players (and my own) asses to become experts at the rules, employing shock collars to arrest deviating conversations, using cattle-prods to keep players thinking about their next action, etc. ... no.

Tagz points are key, though.

I ask these questions because with a group of 6 characters (most have 2 IP and the adept has 3) and 6 baddies (2 IP and the leader had 3), it took over an hour real time for 2 combat turns to complete. These seems like a very clunky way of doing things but I can't seem to see if there is a better way of doing it. Worst is that the players enjoy the role-playing part but are nearly disheartened by the idea of getting into combat, regardless of the reason or motivation of the characters.
Final few points to consider: Unless the characters are constantly going up against elites...elite assassins, elite military/corporate units, etc. then once 1 bad guy dies (or is dropped) there's a good chance the rest will run or surrender. Using glass-jaw henchmen is another way to speed things up. If a minor NPC is hit for physical damage they go down (maybe not dead, but unconscious or cowering) and you could modify this based on the professional rating of the henchmen/minions such that if they take their professional rating or higher in physical damage, then that's when they go down.