It's taken 109 game days but I've got there: 100% Xtreme combat & trade, and 100% maximum race ranks. You can't get the Goner rank to 100%, there is no way to do it, but I've done the rest. I'm super-happy that it's all over now, but it was a lot of fun. I am wondering if I should upload my game stats now, or wait a bit longer until I've finished the rest of my game goals? I've still got things to do, and I think I'll keep playing a little bit longer. Maybe, I'll finish at 115 game days or so. At least that's what I'm thinking of doing.

My thoughts about the experience:
I think that when they were writing X2, the developers (and testers) got the balance of everything just right. Moving up through the fight levels takes time, and it takes increasingly longer to level up at each step. Eventually, the only way to keep your combat rank going up is to kill Xenon and Khaak capital ships, and kill lots of them. You can see your progress with every kill though, and the goal is always in sight.
Getting to Xtreme trade takes far longer, and I'm sure that it would be impossible without the trick of selling weapons to equipment docks that don't stock them. That way, you can build hundreds of weapons forges and have somewhere to sell the weapons they produce. That, along with the addition of somewhat over-powered player ships (namely the pegasus and the Xenon K) kept me playing until I made it to the Xtreme trade rank. The strafe drive is another thing that gives the player an unfair advantage, but without it, and the pegasus, the K and the equipment dock trick, X2 wouldn't be half as much fun.
After I had got to Xtreme combat and trade, I did think about whether it would be possible to get the race ranks to 100%. It's a lot lot harder than getting to Xtreme trader though. At high level, the only two missions that make any difference to the race ranks are XI missions and assassinations. Assassinations give you a lot more than XI missions but it's still very slow going. Once you get to the top tier with a race, it takes roughly between 10 and 20 assassinations for that race to get a further 1% increase. So, to get to 100% for all the races, you need to complete thousands of assassination missions!
Thankfully, assassination missions pay better than all the other missions, with the exception of XIs, so they are worth doing. They are fun too. At Xtreme level, assassination missions spawn an M2 and M6 escorts. The M2s are basically all the same, but the M6s have personality. The Split Dragons go down fast, but they have enough fire power to hurt you, if you are not careful. They are also the only M6s that are a significant threat to your freighters. The dragons often go after your other ships, and it's annoying as hell. The Paranid M6s are not as dangerous as the dragons, but they dodge and weave away from your fire far more than any of the others, so they take the longest to get rid of. Every time one of their pilots says "Now feel the heat of Paranid weapons", I almost burst out laughing. If they had actually brought Paranid weapons with them, I might have been worried! The Hydras are a bit strange, and they are a little bit hard to kill (although not as hard as the Nemeses) because they tend to get quite close, so you have to make sure that you keep your distance to stop them from ramming into you. The Ospreys are tough as anything, but they are so slow that you can get two (or even three) of your K's turrets to lock on to them. Their extra 125MW shield makes no difference when you can hit them with that much firepower. Like the dragons, they have enough fire power of their own to hurt you though, if you're not careful. You can sometimes lock three turrets onto Centaurs too, but that doesn't usually happen. They are more often than not dead before all the turrets can lock on. The Centaurs are cannon-fodder, and have no redeeming qualities! I'm extra happy when an assassination mission is for an Argon target: the mission is super-easy and usually over very quickly. You can do the assassinations OOS too, and I usually do if the target spawns in a different sector. You still get the same reputation points for the kill. You need to watch the combat though, otherwise there's a much larger chance of losing one of your ships.I've found that two Ks work well for doing this. If you make sure they are attacking together, and at least one of them is targeting the M2, it works just fine. With the Teladi, you'll need both Ks attacking the M2, and even then you can still lose a destroyer occassionally (but it doesn't happen very often). Just make sure you save before the start of the fight. You have to micro it a bit as well: once the M2 dies, you'll need to re-issue the attack order, otherwise your Ks will just sit there and let the M6s destroy them.
Even though getting the 100% race ranks was the main goal of my game, I'm not finished yet. Over the last year or so, I've made a few other goals that I want to complete. Those are going to take some time too. I won't add any more new goals though, I want to play X3 and X4 now, so I can't let my X2 game take too much longer...