A good quality 5W/40 car oil is fine for a Suzuki GS125. The redline isn't particularly important; what matters is the stress the oil is subjected to. In fact, a lot of car oil meet the Japanese factories specifications for a minimum of API-SE standard oil for their bikes.
Can I use a good quality car engine oil in my Suzuki GS125? Or is the 10,000rpm redline too high for it? If I can use it, will I have to change oil more often than the owner's manual suggest? The bike has a 4-stroke engine.