Well, "fast enough" is pretty vague. But bear in mind that Minecraft has never seemed to care about optimisation. For the longest time it was still running Java 7 even when Java 8 with the G1 collector had been out for a long time, and improved performance quite a bit.

HotSpot has a pauseless GC these days from Red Hat and is getting another one developed by the Java team itself, so even Minecraft's very heavy use of GC should be ok (heavy, after the new devs "improved" Notch's code to use objects everywhere instead of passing coordinates in separate parameters).