Sure traffic shaping is quite CPU intensive, so not using SQM will leave cpu cycles for other things. But I have no experience with WG so can not give you any guidance about its cpu-hunger.
But I would be amazed if your current router would allow WG in the gigabit range...
Have a look at Jeff's excellent performance tests, I believe your current router should be roughly equivalent to either the ramips or one of the ath79 platforms in Jeff's result pages...
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