Which Nmap option would you use if you were not concerned about being detected and wanted to perform a very fast scan?

-T0 is the 'paranoid' timing template that introduces very long delays between probes specifically to evade IDS detection, which is the opposite goal of a fast, unconcerned scan.

The -T5 'insane' template sets the most aggressive timing parameters available in Nmap - minimal inter-probe delays, maximum parallelism, and the shortest response timeouts - completing scans as rapidly as possible. Because it generates a high volume of packets in a very short time, it is highly visible to any IDS or traffic monitoring system. It is the correct choice when scan speed is the sole priority and detection is completely irrelevant.

-O enables OS detection by analyzing TCP/IP stack fingerprints and has no effect on scan speed or stealth level.

-A enables aggressive mode bundling OS detection, version detection, NSE script scanning, and traceroute together, but it is not a timing control and does not maximize raw scan speed.