Welcome to the forums, OhJoy. :-) Credit questions can be broadly divided into theoretical and practical. Theoretical questions are asked purely for the sake of being a credit score hobbyist. You don't actually need to know the answer, it won't help you do or achieve anything important to your finances, etc. -- the hobbyist asks because he is purely interested (in a geeky way) at guessing the abstract workings of the scoring algorithms. Practical questions are asked because you need to raise your score so you can do something: get approved for a car loan, get better rates on PMI, etc. The question about whether some of FICO's models might give you some small benefit for having a mortgage, such that without such a mortgage you could only get up to (say) an 845 -- this is a theoretical question. It has no practical importance, because nobody needs an 850. Lenders stop caring what your score is once it is over 780. (Arguably 760.) It sounds like you are much more interested in the practical nuts and bolts of how to achieve a 760. If so, forget about buying a house as a credit score raising strategy. That would be a terrible idea. Only buy a house because you want that house. Actually, getting a mortgage will typically lower your FICO 8 and FICO 9 scores for the first decade or so -- or as long as it takes to pay a significant chunk of it off. That's as compared with having a single small loan that is mostly but not entirely paid off. As far as improving your score, the only thing you need to do is get the derogs off and wait. And of course keep making payments on time on your loans. Should you end up with a huge amount of extra cash (a relative dies and leaves you 12k) you can improve your score by paying your loans down but still keeping them open for the full term. One thing you should not do (if you want to improve your score) is open more cards. Also avoid any CLI requests that could result in hard pulls. You have plenty of cards and increasing your credit limits will not help your score.
Thanks for the welcome 
So, I have a new car loan and a secured installement loan totaling around $13,600. If I put my hands on $12K (without someone dying, that is), should that pay off the small loan and the rest on the car? Or, keep them both open and take them both down to 9%? Surely that would really boost my scores.
Perfect! Thank you for explaining that and estimating the point value.
Totally possible.. Here is a snapshot of TU score with profile. FICO8 score 850
IMO a score of 850 is just a cool, factor. It is all gravy after 780 IMO. I am sure with a profile of 3 to 4 credit cards with 3% or lower UTI, 1 installment loan paid down to 9%, and 7 or 8 years AAoA, no negative info would get anyone at or very close to 850 FICO8 score.
Another point I can make is, I have not hit 850 on my EX or EQ with the same profile with the exception of one account. The only real difference is a 33yr old AU revolving trade line, clean with 0 balance. However FICO8 is discounting the AU card in their scoring anyway. So, IMO each reporting agency has a little variation in their FICO algorithm.
Number of Accounts: 9
Revolving accounts open: 5
Revolving accounts closed: 3
Revolving utillization: 0.5%
Average age of accounts: 5.7 years
Age of oldest open Account: 31 years
Installment accounts open: 1 (This is a shared secured loan)
Installment accounts closed: 0
Installment utilization: 8.6%
Inquiries: 0
Negative reporting: 0
Admittedly, there is one unusual trade line and one FICO scoring strategy trade line. Highlighted in RED.
1. I have a very old department store credit card joint account holder on. This is getting me extra points in the AooA portion of my credit score. Not sure how many points this is adding to the score, but it is a little point kicker.
2. I have only one installment loan of $500 that is paid down to below 9% utilization. This is Share Secured Loan strategy pioneered by many people on the forum. This is probably worth 30 points on the scoring model.
