Over the years, I have purchased custom systems from Falcon Northwest and MAINGEAR.
Both companies offer outstanding build quality but are very expensive.
I suggest you look at the configuration pages on their websites. You indicated that your price point is "under $4500".
Both companies can configure very powerful systems for much less than that. From my experience, the sales people at these companies will offer very helpful advice and will not try to upsell you. I configured systems for considerably more than the sales advisors recommended and ended up saving money after working with them on the configuration.
Last, the other important thing you are paying for in buying from a high end system builder is technical support. My experience with both could not have been better.
I have not dealt with the other companies you mentioned which may be just as good and there are other options you can research.
Good luck
Another factor to consider is technical support