I've just tried on a go binary that was 2.4MO. After building it with `go build -ldflags=-s .`, it's 1.6MO. After stripping with upx, it's 480ko (and still works, and has panic stack traces).
When downloading a WASM file over HTTP, the server can gzip it transparently. It'd be interesting to compare the effects on the size with what upx does (which is more specialized than gzip).
Indeed, given how browsers already handle gunziping resources, it's probably best to rely on it. My binary, stripped by the go compiler and gziped, is 525ko (against 480ko using upx).