It really depends. There are enough flex points spread throughout that you can really tailor the character. The Slow Learner trait is also a major obstacle, so if its gotten rid of, the final result can change. Also, all this is assuming a Clan Trueborn MechWarrior going through Creche, Sibko, ToD:Clan.

Looking at the basics, you can get 95 points from a Trueborn Sibko. Tour of Duty: Clan doesn't specifically give you Piloting and Gunnery, but since it gives you +25 to 10 of your Field Skills, and you only have 12 Field Skills (Clan Basic Training and Clan MechWarrior), I'm going to assume you put 25 points into the two skills. So that puts you at 120 points.

120 points is a +3 with the Slow Learner Trait, but a +4 on the "Standard" skill chart, and a +4 if you somehow get Fast Learner.

If you dump all the flex points you can into the skills (15 each from Trueborn Creche, 25 each from Trueborn Sibko, and 50 each from Tour of Duty:Clan), that bumps it up to 210.

210 nets you a +5 from the Standard chart (20 points shy of a +6) and the Slow Learner chart. The Fast Learner has already bumped up to a +6.

I'm going to say the average is somewhere between +4 and +5. +4 with Slow Learner is only 144 points, and without spending any flex points, you've already reached 120 as shown above. Spending another 24 each isn't that much of a strain on your points. If you manage to buy off Slow Learner, 120 is a +4 as well, with +5 coming in at 170, only 50 points away.

Hope that's not too confusing.