Big Air: A 3203 bearing to you and me is dimensionally identical to a 5203 (ID, OD, width). The difference is the 3203 is a newer design, made from extremely high quality bearing steel with much reduced impurities and better grain structure, better heat treatment for improved dimensional stability (up to 300 °F), internal geometry design changes that are less sensitive to axial overloading, races manufactured to ISO P6 running accuracy, ball uniformity manufactured to one ISO grade better than SKF 5203 (several grades better as compared to other brands like BDX Peer) which improves running accuracy at high speeds (reducing noise and operating temperature), improved Polyamide cage to better withstand high acceleration. Those changes resulted in lab-tested load-carrying performance improvement, increased durability (similar axial wear at 40,000 hours vs. 1000 hours), higher reliability, and longer service life (tested at double vs. SKF 5203 - more for other brands).
In my opinion, an SKF 3203 in a critical application like this, in $800 DD, in a $10,000 sled, which could ruin a cool ride if it grenades - is well worth the extra $20 cost vs. a Chinese Peer (BDX) 5203 bearing.
You can purchase a SKF 3203 for about $35 at a local industrial power transmission store, ebay or amazon.
Good luck!