It's still fast enough that I wouldn't worry about it.
Once you blitz through all the free space on the drive, it will slow down a bit, but not enough that it will make a real-world difference. For what it's worth, the Kingston drive in my current machine at work gets 6.4 on one run and 7.1 on a subsequent run of winsat. The numbers aren't that reliable unless your PC is actually doing nothing, but there are too many services doing background IO on most Windows installations to truly benchmark an OS drive reliably, you need to test it as a secondary drive to get a realistic value without interference during the benchmark by the OS.
You should install Samsung Magician if you don't already have it and then perform the steps it recommends to optimise Windows for the SSD, it also gives you a whole bunch of SMART info and stats, drive health and lets you benchmark your drive against what its rated specs are, so if it's way out on one of those you can investigate further.
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