Unfortunately, there is no direct correlation between file size and MEMORY usage with STEP.
I've opened larger STEP files on an 8GB machine before. Took a VERY LONG TIME but opened nonetheless.
What kind of error are you seeing?
I wouldn't get errors so much as it will run for 24 hours plus and then stall out. While opening it would add small 13MB Part files into the folder that the stp file is stored in. There would be iterations of parts with the same name with a new number at the end of the file, thousands of them, then it would change the base name and start adding iterations of the next file, all roughly 13MB in size. Then, it would start adding small assembly files mixed in with more part files until it eventually totally stalls out. One file had created 35,000 files before it stalled.
files with less than 1500 components open without a problem, but over that is gives a window saying that the file will be created on disc because it's over 1500 componenets. I haven't been able to get any file being created on disc to complete yet. Any advice on opening settings for stp files that could control that? What would be best for forming solods, b-rep mapping, knit surfaces, merge entities, showing IGES levels etc?