That sounds about right, mine is a SC model as well and can hit upwards to almost 80C. I applied MX-2 on the core and whatnot as there was an abundance of the old stuff and it has helped slightly.
Last couple of days I've had the GPU temp and fan speed on my G15 so I can monitor it in games; L4D seems to bring up the temps like no other, but the auto fan setting compensates trying not to let it go too much above 80C. Has gone up to 80% for a few seconds too, highest I've seen.
I would not recommend leaving a static value like 50-60% when you are in games. At 56%, which is audible for me, it has gone up to ~95C during L4D. It also doesn't help that my card does not revert back to 2D clock modes until I reboot when Steam is running (181.22s).