sys_memory should be somewhat smaller than the memory in your task manager.

sys_memory is the sum of all memory allocations by the engine, and depends on what you have in your level and scripts. The task manager memory is the overall consumed memory by the process. It is calculated by Windows, while sys_memory is calculated by the engine. sys_memory is a var and thus can not (and should not!) exceed 1 GB.

If you have huge discrepancies between both, you're maybe doing things that consume memory but don't affect sys_memory - for instance, opening new tasks, loading DLLs or something like that. Make some tests, for instance load your levels without script or your script without level, and check where the discrepancies come from.